FY.Bsc. Paper I / Term II Zoology Chapter 3 – Study of Frog 1) Rana
FY.Bsc. Paper I / Term II Zoology
Chapter 3 – Study of Frog
Multiple Choice Questions
1) Rana tigrina is a member of the order
A) Lepospondyli
B) Anura
C) Apoda
D) Urodela
Answer is ‘B’
2) The frog swims in water by:
A) Powerful forward thrusts of its forelimbs.
B) Powerful backward thrusts of its forelimbs.
C) Powerful backward thrusts of its hind limbs.
D) Powerful forward thrusts of its hind limbs
Answer is ‘C’
3) The tongue of frog is
A) Short, protrusible and attached at the front end.
1 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology B) Short, protrusible and attached at the distal end.
C) Long, non-protrusible and attached at the front end.
D) Long, protrusible and attached at the front end.
Answer is ‘D’
4) During hibernation or aestivation frog lives upon:
A) Stored glycogen and fat.
B) Stored glucose and fat.
C) Stored starch and fat.
D) Stored galactose and fat.
Answer is ‘A’
5) In frog, the sexual embrace between male and female is called:
A) Spawning
B) Swarming
C) Aplexus
D) Amplexus
Answer is ‘D’
6) Opening of rectum in frog is termed as
A) Coccyx.
B) Anus
2 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology C) Cloaca
D) Rectum
Answer is ‘C’
7) Teeth in frog are
A) Acrodont
B) Homodont
C) Polyphyodont
D) All of the above
Answer is ‘D’
8) The chief nitrogenous waste material in the urine of frog is
A) Ammonia
B) Uric acid
C) Urea
D) Trimethylamine
Answer is ‘C’
9) Which of the following differentiates male frog from female frog?
A) External nares
B) Brow spot
C) Nuptial pad
3 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology D) All of the above
Answer is ‘C’
10) Male frog can croak louder than females because being
A) Stronger
B) Larger in size
C) Larger sound box
D) Vocal sacs
Answer is ‘D’
11) Bidder’s canal is found in
A) Kidney of male frog
B) Kidney of frog
C) Testis of frog
D) Liver of frog
Answer is ‘A’
12) In frog tangoreceptors respond to
A) Heat
B) Touch
C) Chemicals
D) Smell
4 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Answer is ‘B’
13) Some frogs hibernate during the winter and avoid the harmful effecting of freezing by accumulating and glycerol in their bodies
A) Fat
B) Thyroxine
C) Sebum
D) Glucose
Answer is ‘D’
14) The frog most commonly used in zoology laboratory for dissections, and is also the frog that has the widest distribution, belong to the genus.
A) Genus Hyla
B) Genus Bufo
C) Genus Rana
D) Genus Sirenia
Answer is ‘C’
15) Suitable breeding season in frog is
A) Winter season
B) Rainy season
C) Spring season
D) Summer season 5 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Answer is ‘B’
Answer the Following ( 2 Marks
Q.1. Explain in short the habitat of Frog
Ans:
Frogs are non- poisonous , harmless and normally silent animals
Frogs are found near water and in or near water (fresh water lakes, ponds and streams) and in very damp places of land.
It lives in water, to keep the skin moist to carry on cutaneous respiration and to jump or slip into water to escape from enemies.
Q.2. What is the food of the frog?
Ans:
Frogs are carnivores. Smaller frogs eat insects such as flies, mosquitoes, moths and dragonflies.
Larger frogs will eat larger insects like grasshoppers and worms.
Some large frogs will even eat small snakes, mice, baby turtles, and even other smaller frogs
Most frogs will starve before they eat a dead insect or animal.
6 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Q.3.Define portal system (March – 2013)
Ans:
The veins, which start with capillaries in the organ from where they collect blood and then end or break up into capillaries in certain other organs, are known as portal veins, and this system is known as portal system.
The name portal vein and the portal system portal is usually based upon the name of that particular organ into which it finally breaks up.
In frog, there are two portal systems
Renal portal system (ii) Hepatic portal system
Q.4.What is a Nictitating membrane?( March – 2013)
Ans:
Nictitating membrane:
The 'third eyelid', a thin, transparent fold of skin at the inner angle of the eye or below the lower eyelid that can be drawn across the eyeball for protection without obscuring vision
This membrane closes over the eye whenever the frog is in or under the water. It can also flick across the eyes when the frog is out of the water, performing a useful function by cleansing and moistening the surface of the eye.
Q.5. What is the Posture of the frog while floating in water?(March – 2013)
Ans:
7 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology When the water of pond is very deep, the frogs float on the surface.
In the floating posture, the rest of the body lies quiet, hanging obliquely with the hind limb moderately extended with the nostrils above the water for breathing
Q.6. Explain Anura( March -2011)
Ans:
Anura:(salientia; anurans, tail-less amphibians, frogs and toads;
An order of amphibians in which the head joins directly into the trunk.
The vertebral column is short and there is no tail in the adult.
The fore limbs are stout and long, webbed.
hind limbs are used for jumping and swimming.
The eyes are large and high on the head.
There are superficial ear membranes posterior to the eyes.
All anurans lay eggs, have external fertilization, and develop from tailed tadpoles. There is no *neoteny. ‘Sexualdimorphism is common.
The males often being smaller and having vocal pouches.
There are 2600 species, widespread Iintropical and temperate zones.
Answer the Following (5 Marks )
8 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
Q.7. Give the general characteristics of Amphibians
Ans:
General characters of Amphibians are:
1) Amphibians are cold blooded vertebrates which can live on land and in water.
2) Amphibians show four limbs with which they can swim in water and jump or walk on the land, (But In apoda limbs are absent.)
3) In Amphibians animals exoskeleton is absent. But in apoda animals small cycloid scales are present.
4) In Amphibians the adult animals lungs are present. Gills are absent. But In some urodelans the gills are present.
5) Amphibians Skin is a respiratory organ.
6) The Amphibians skull is dicondylic.
7) Amphibians Ribs are absent.
8) In Amphibians The body divisible into head and trunk Tail is present.
9) Amphibians Digestive system is well developed. A well developed liver Is present.
10) External ear is absent. Middle and inner ears are present, the middle ear columella auris Is present.
9 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology 11) Amphibians Heart is 3 chambered with 2 auricles and 1 ventricle The blood contains R.B.C. They are nucleated. They contain hemoglobin.
12) Blood vascular system contain hepatic and renal portal systems.
13) Amphibians Kidneys are mesonephric. Urinary bladder is present. It stores urine.
14) Central nervous system is well developed. The brain occupies completely the cranial cavity. The brain is divided into fore, mid and hind brains. Brain continuous as spinal cord.
15) 10 pairs of cranial nerves will arise.
16) Sexes are separate.
17) Male and female can be indentified - Sexual dimorphism.
18) In Amphibians the life history a larva stage may be present.
19) Amphibian Eggs are telolecithal, Cleavage is holoblastic unequal.
Q.8. Give the systematic position of frog
Ans:
Systematic position of frog:
Phylum: Chordata
Subphylum: Vertebrata
Division: Gnathostomata
Superclass: Tetrapoda
Class: Amphibia
10 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Order: Anura
Suborder- Diplasiocoela
Family – Ranidae
Type: Rana Tigrina
Q.9. Describe the habits of frog.
Ans:
Some of the habits of frog are described below.
1) Locomotion: Frog moves in two ways (i) by leaping on land and by swimming in water.
(i) Leaping:
It jumps or leaps by extending the hind limbs, which act like springs throwing the body up into air.
A frog may leap a distance of 1.5 to 2 meters in a single jump.
On landing back the forelimbs act like shock absorber.
The forelimbs also manipulate and adjust the direction of the jump.
(ii)Swimming:
The frog swims in water by powerful backward thrusts of its hind limbs which act like propellers.
During their backward strokes, the toes are spread apart and the broad webs push against water, moving the body forward.
11 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology 2) Feeding:
Frogs are carnivorous and food consists mainly of living insects, worms, mollusks, and tadpoles.
The food is not chewed but swallowed whole.
3) Croaking:
The characteristics noise or sound made by frogs is known as croaking.
It is commonly heard in breeding season which is a mating call.
Frogs can croak under the water and on land.
4) Hibernation and aestivation:
Body temperature of frogs fluctuates with environment.
During adverse environmental conditions in cold winter or dry hot summer days, they burry in the soft damp bottom mud for protection. .
They become metabolically inactive and stop feeding, living on glycogen and fat stored in the body.
This state of dormancy is called as hibernation, which occurs in winters and aestivation occurs in summers.
5) Camouflage:
Frogs are not easily noticeable by their enemies as they can change the colour of their skin to match that of the environment.
This type of protective colouration is known as camouflage.
12 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
6) Breeding:
During rainy season, frogs emerge out of aestivation and immediately start breeding which lasts from July to September.
Males gather in appropriate shallow waters and start croaking justly to attract females for mating or copulation.
7) Enemies:
Several natural enemies eat adult frogs and tadpoles thus reducing, their numbers.
Frogs also serve as hosts for different kinds of parasites.
8) Economic importance:
It is used for laboratory study more often than any other animal as a vertebrate type.
It is a good friend of farmers as it feeds on insects harmful to crops.
Q.10. Explain the sexual Dimorphism in frog.
Ans:
sexual dimorphism, is the differences in appearance between males and females of the same species,
There are some differences in external characters by which male and female frogs can be distinguished. Such as 13 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology 1) Males are smaller and darker in colour than females.
2) Males are slimmer while females are stouter, especially when they contain eggs.
3) Males croak loudly as they have vocal sacs which are absent in females. The eardrum is larger in male.
4) Males have swollen copulatory or nuptial pads on inner fingers , especially developed in breeding season for grasping the females during mating. Nuptial pads are lacking in females.
5) In copulating , frogs in amplexus, the upper one is male and the lower one is female
Q.11. Describe the feeding and Physiology of digestion in frog
Ans:
Frog is carnivorous
It feeds on insects, worms , crustaceans , mollusks , small fishes , small frogs and tadpole. 14 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Prey is captured by flicking action of tongue and swallowed whole without mastication.
The food is passed down the oesophagus into the stomach.
Mucus helps in lubricating food.
1) Gastric digestion:
Food stays in stomach for sufficient time ( 2 to 3 hours)
The gastric containing hydrochloric acid and enzyme pepsinogen secreted by the gastric glands of stomach ,aid in hydrolysis of proteins , breaking them into peptones and proteoses.
Acid secreted kills the bacteria and fungi present in food making it soft.
Muscular contraction of stomach wall aid in disintegration and mixing of digestive enzymes with food.
When the liquefied semi digested acidic food, now called chyme, reaches the proper state, the pyloric sphincter relaxes allowing the chyme to enter duodenum.
2) Intestinal digestion:
Presence of chyme in the duodenum causes production of several intestinal hormones, like
(i)Enterogastrone –reaches stomach through blood to stop the production of more gastric juices with HCl.
(ii)Cholecystokinin- causes gall bladder to contract and release bile into duodenum.
15 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology (iii) Secretin and Pancreozymin together stimulate pancreas to secrete pancreatic juices into duodenum.
(iv) Enterocrinin activates secretion of intestinal juice. The succus entericus.
The important substances mix up with food in intestine, necessary for completion of digestion.
3) Absorption:
Absorption of final products of digestion occurs through the wall of the intestine.
Folds with villi-like processes increase the internal absorptive surface.
Water, mineral salts and other nutrients in solution are directly absorbed through the epithelial lining.
Carbohydrates are absorbed as glucose and fructose, while proteins as amino acids.
These pass into blood capillaries in the folds, then into hepatic portal system and into the liver.
Fatty acids and glycerol pass into lymphatic capillaries or lacteals in the folds and so into the veins.
4) Assimilation:
Absorbed food is used for two basic purposes of nutrition.
(i)Liberation of energy during respiration and
(ii)Assimilation as a part of intimate structure of the animal.
16 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Surplus glucose may be either stored as glycogen in liver or skeletal muscles, or converted to fat or incorporated in living protoplasm.
Fatty acids and glycerol are converted into fats which are deposited in adipose tissues.
Amino acids forms proteins for growth and repair or undergo deamination resulting in the formation of urea to be excreted by kidneys with urine.
5) Egestion:
Undigested part of food is slowly moved by peristalsis into rectum for storage and preparation of faeces.
At intervals the faecal matter passes into cloaca and egested through cloacal aperture.
Q.12. Describe the sense organs in frog
Ans:
The sensory system includes receptors or sense organs.
These receive sensation or stimuli due to change in the external or internal environment.
Frog has five senses like touch, smell, taste, sight and hearing.
1) Organs of touch or tangoreceptors:
17 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Frog has numerous cutaneous sense organs or tangoreceptors present under epidermis of skin.
These are either in the form of simple network of nerve endings scattered among cells or as compact groups of cells forming corpuscles projecting into papillae of epidermis.
They are sensitive to various types of stimuli such as touch, chemicals, temperature. Humidity, light, pain etc
2) Organs of taste or taste buds:
Gustatoreceptors or taste organs are in the form of taste buds present in small papillae on the tongue and on the floor and roof of buccal cavity.
A taste bud consists of elongated spindle- like receptor cells or taste- cells ending in fine hair- like processes for sampling food which is taken in mouth.
3) Organs of smell or olfactory organs:
Epithelial lining of two nasal chambers forms the olfactoreceptor or the organ of smell.
It contains tall olfactory receptor cells with tufts of fine cilia on their outer ends and nerve fibres attached to their inner ends.
4) Organs of sight or eyes:
Photoreceptors or the organs of sight are the two large eyes, similar in general structure and function with those of the vertebrates.
Each eyeball is roughly spherical and lodged inside an orbit in the dorso-lateral side of head protected by eyelids.
18 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology 5) Organs of hearing or ears:
Statoacoustic organs meant for hearing and equilibrium are a pair of ears attached to skull postero-laterally in all vertebrates.
An ear of frog consists of only two parts, middle and internal ear .
There are no external ears.
Q.13. Discuss the blood in frog and give its function
Ans:
Blood is the chief circulatory fluid of the body.
It contains a clear liquid called plasma, in which are suspended various types of free cells , called blood corpuscles.
1) Plasma:
Plasma forms nearly two-third part of blood.
It contains 90% of water in which are dissolved mineral salts , absorbed foods ( sugars, proteins) excretory wastes ( urea) , secretions ( hormones) and other soluble substances.
2) Corpuscles:
Blood cells or corpuscles are mainly of three types
(i)Erythrocytes or red blood corpuscles:
19 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology These are oval , flattened, nucleated and biconcave in shape They bear the respiratory pigment hemoglobin, which serves as an oxygen carrier.
(ii) Leucocytes or white blood corpuscles:
These are colourless, nucleated and mostly amoeboid cells of at least five types.
Most of them are phagocytic, ingesting bacteria and other foreign particles that appear in blood. And also remove dead old tissue cells.
The WBC of frog are Lymphocytes, monocytes and granulocytes.
(iii)Thrombocytes or blood platelets :
These are small ,nucleated ,spindle cells playing an important role in coagulation.
Functions of blood in Frog:
1) The functions of frog blood cells are carrying oxygen and nutrients to cells and taking waste and carbon dioxide away from cells.
2) Blood cells also heal the skin when cut and fight diseases that come into the body.
Q.14. What is gametogenesis? Describe the spermatogenesis in frog (April-2011)
Ans:
Gametogenesis: Process of formation and maturation of gametes (sperm or ova) is called gametogenesis. It occurs in gonads (testes and ovaries). The term gametogenesis includes both spermatogenesis and oogenesis. spermatogenesis or the formation of sperms, occurs in the testes and oogenesis or the formation of ova,occurs in the ovaries. 20 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Spermatogenesis: Production of sperms, which takes place in the testes is known as spermatogenesis.
Spermatogenesis is frog:
When the photoperiodism is appropriate during breeding season, the given cells undergo spermatogenesis within the testes.
During this period, the walls of the seminiferous tubules produce spermatogonia which go through mitotic divisions and then the series of nuclear charges without mitosis.
This results in the appearance, toward the lumen of each tubule, of clusters of mature spermatozoa.
The spermatogonia are found close to the basement membrane of the seminiferous tubule.
These then await their turn to undergo, the maturation changes necessary for the production of spermatozoa which will be ready for the breeding season.
The elongated and filamentous tails of the clustered mature spermatozoa project into the lumen of each seminiferous tubule.
At the peak of spermatogenetic activity, all the stages of maturation from the spermatogonium to the spermatozoon are present.
The spermatogonia are always located around the periphery of the seminiferous tubule and are small, closely packed cells, each with a granular, oval nucleus.
In between the spermatogonia may be found occasional very large cells, the primary spermatocytes.
21 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology These tend to be irregularly spherical, possessing large and vesicular nuclei.
Apparently they divide to form secondary spermatocytes almost immediately, for they are so few and far between.
The secondary spermatocytes are about half the size of the primaries, and lie toward the lumen of the tubule.
They generally have a darkly staining nucleus, and the cytoplasm may be tapered toward one side.
The spermatid, following another division, is even smaller and possesses a condensed nucleus of irregular shape.
Clusters of spermatids appear as clusters of granules, the dark nucleus being almost as small as the cross section of a sperm head.
During the metamorphic changes from spermatid to spermatozoon, The inner of the two spermatid centrioles passes into the nucleus , while the outer one give rise to the tail like flagellum.
22 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Frog T.s of testis.
The mature spermatozoon averages about 0.03 mm. in length.
It has an elongated, solid-staining head (nucleus) with an anterior acrosome, pointing outwardly toward the periphery of the seminiferrous tubule.
The short middle piece generally is not visible but the tail appears as a gray filamentous extension into the lumen,about four or more times the length of the sperm head.
The mature spermatozoon is dependent upon external sources of nutrition so that it joins from 25 to 40 other spermatozoa, all of whose heads may be seen converging into the cytoplasm of a relatively large, columnar-type basal cell known as the Sertoli cell.
This is functionally a nurse cell, supplying nutriment to the clusters of mature spermatozoa until such time as they may be liberated through the genital tract to function in fertilization.
23 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Frog Spermatozoon
Q.15. Discuss the Oogenesis in frog
Ans:
In frog, the process of ooggenesis involves the following phases.
1) Premeiotic or multiplication phase 2) Growth phase 3) Maturation phase
1). Premeiotic or multiplication phase:
Ova frog is derived from the primordial germ cells that enter into the ovary at an early stage of embryonic development.
The primordial germ cells divide mitotically and produce a large number of oogonial cells, which divide through mitosis several times and then stop dividing.
Some of these cells grow in size and are called primary oocyte.
The oogonia which fail to grow become follicle cells.
These surround the primary oocyte. Such a group of follicle cells and the oocyte is called ovarian follicles.
Each ovary consists of hundreds of such follicles.
2) Growth phase:
As the ovum contributes all nutrients and other materials required for the development and growth of embryo, the primary oocyte undergoes a prolonged growth phase, and increases in size considerably.
24 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology The differentiation of the ovum also occurs along with the growth.
Infrog, a young oocyte measures about 50 μm in diameter, and the fully developed ovum in different species measures from 1000 to 2000 μm in diameter.
Rate of growth of oocytes varies in different animal species.
In Rana pipiens the growth phase continues for three years.
The young primary oocytes start growing after the tadpole metamorphoses into a young frog.
The young frog does not lay eggs upto the age of two years.
It lays eggs only in the third year.
Every year a new batch of oocytes is produced by the oogonial divisions. Every batch of eggs matures in three years.
The oocytes grow slowly for first two years, but grow rapidly in the third year.
The growth phase of the oocytes may be divided into two stages :
A) Previtellogenesis
B) Vitellogenesis.
A)Previtellogenesis (before yolk formation) :
During this period of growth, the size of the nucleus and amount of the cytoplasm of oocyte increase.
B) Vitellogenesis(yolk deposition ) :
25 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Formation and deposition of yolk, or vitellogenesis, occurs in the oocytes during the second period of growth.
Oocytes grow rapidly during vitellogenesis
In amphibian eggs, the yolk is found in the form of large oval granules, called yolk platelets.
Yolk is the reserve food of the ovum. In amphibians, yolk platelets contain two main proteinaceous substances: phosvitin and lipovitellin.
Phosvitin is a highly phosphorylated protein, and lipovitellin contains proteins and bound lipids.
3) Maturation Phase:
The diploid primary oocyte undergoes first meiotic division in the beginning of the growth phase.
This result in small cell called the first polar body and large cell called secondary oocyte.
The second phase of the meiotic division occurs, resulting smaller cell called second polar body.
The larger cell is now called the mature Ovum.
In the meantime, the first polar body may divide into two
Thus at the end , four cells are produced from one oocyte.
One haploid ovum and three haploid polar bodies.
The polar bodies soon degenerate. 26 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
Q.16. State the difference between Spermatogenesis and Oogenesis( April -2011)
Ans:
Spermatogenesis Oogenesis It occurs in the testes It occurs in the Ovaries Growth phase is short ,so that Growth phase is very long , so that spermatocytes are only twice the size of oocytes are much larger than oogonia spermatogonia Oocytes have cytoplasm rich in RNA, ATP, Spermatocytes have cytoplasm and enzymes and yolk and nucleus with giant chromosome and large nucleoli nucleus with normal contents A primary spermatocyte divides equally to A primary Oocyte divides unequally to form form two similar secondary spermatocytes one large secondary Oocyte and one Minute polar body. A secondary spermatocyte also divides A Secondary Oocytes also divides equally , forming two similar spermatids unequally, forming one large Ootid and one minute polar body. Upto the formation of spermatids , the cells Oogonia are separate and surrounded by often remains interconnected follicle cells.
A spermatogonium produce four functional An Oogonium produces one functional spermatozoa ovum and three non- functional polar bodies. Spermatozoa are minute streamlined, Ova are much larger, rounded often with yolkless and motile. yolk and non- motile.
Spermatogenesis is often a continuous Oogenesis is not necessarily a continuous process process
Spermatogenesis is usually completed in Oogenesis is often completed in the the testis, so that mature sperms are reproductive tract of the female. Or even in released water as Oocytes leave the ovaries
27 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Q.17. Write a short note on hibernation and Aestivation ( April – 2011, April -2009 , Oct – 2011 , April -2012)
Ans:
Hibernation:
Hibernation is a phenomenon of amphibians living in temperate regions, where the low ambient temperature of winter is adequate to raise their own body temperature sufficiently to allow activity.
After an animal finds or makes a living space (hibernaculum) that protects it from winter weather and predators, the animal's metabolism slows dramatically, so it can "sleep away" the winter by utilizing its body's energy stores.
Aquatic frogs such as the leopard frog (Rana pipiens) and American bullfrog (Rana catesbeiana) typically hibernate underwater.
Terrestrial frogs normally hibernate on land. American toads (Bufo americanus) and other frogs that are good diggers burrow deep into the soil, safely below the frost line. Some frogs, such as the wood frog (Rana sylvatica) and the spring peeper (Hyla crucifer), are not adept at digging and instead seek out deep cracks and crevices in logs or rocks, or just dig down as far as they can in the leaf litter. These hibernacula are not as well protected from frigid weather and may freeze, along with their inhabitants.
Aestivation:
Aestivation is similar to hibernation. It is a dormant state an animal assumes in response to adverse environmental conditions, in this case, the prolonged dry season of certain tropical regions.
28 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Several species of frog are known to Aestivate. Two of the better-known species are the ornate horned frog (Ceratophrys ornata) from South America and the African bullfrog (Pyxicephalus adspersus).
When the dry season starts, these frogs burrow into the soil and become dormant. During the extended dry season, which can last several months, these frogs perform a neat trick: they shed several intact layers of skin, forming a virtually waterproof cocoon that envelopes the entire body, leaving only the nostrils exposed, which allows them to breathe. These herpetological mummies remain in their cocoons for the duration of the dry season. When the rains return, the frogs free themselves of their shrouds and make their way up through the moist soil to the surface.
Q.18. Give the functions of the skin in frog.( Oct-2011)
Ans:
The skin of frog has a variety of functions such as
1) The skin provides a protective body covering which protects the underlying muscles.
2) It acts as a germ proof covering and protects the body against foreign germs.
3) The mucus makes the skin slippery which protects the animal by securing release from the enemies.
4) The mucous and poison glands secrete disagreeable and unpleasant fluid which protects the animal from enemies.
29 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology 5) The skin also provides protective colouration due to dispersion of chromatophores under the influence of neurohumours secreted by the nerve endings. Thus the animal can adapt according to surroundings and is well protected.
6) The thin, smooth, moist and highly vascular skin is the main respiratory organ of frog. During hibernation and aestivation the skin is the only respiratory organ to keep the animal alive.
7) The skin is an effecient sensory organ which is sensitive to stimulation, temperature, humidity etc.
8) The casting of stratum corneum in the form of keratin removes the excretory matter of the body.So the skin is also regarded as excretory in function.
9) The mucous glands keep the skin moist and protect the animal against asphyxiation,
10) The frog does not drink water. The water balance of the body is maintained by absorption through the skin.
11) The skin in frog also helps in locomotion and swimming. The hind limbs are webbed which enable the animal to swim.
12) The skin of frog is also regarded as helpful in nutrition. It is considered that the skin is capable to secrete an enzyme, the diastase which digests certain carbohydrates.
Q.19. Explain vocal sac and Cloaca( April-2009)
Ans:
Vocal sac:
30 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology These are the sound-resonating throat pouch of male frogs and toads
Vocal sacs are outpocketings of the floor of the mouth, or buccal cavity.
Frogs display three basic types of vocal sacs: a single median throat sac, paired throat sacs, and paired lateral sacs. (Lateral sacs are located just rearward of the angle of the jaw on each side of the head.)
All three types, whether single or paired, open into the buccal cavity by paired slits.
Each slit is located on either side of the base of the tongue.
A calling frog typically inflates his sac or sacs prior to calling or simultaneously with the production of the first call.
The sac is inflated with air from the lungs.
If another call is forthcoming and the male frog is not in the process of calling, air is still held in the sac.
Sound is produced by a controlled rush of air through the larynx and across its vocal cords.
The resulting sound vibrations are amplified by the resonating qualities of the vocal sac or sacs.
frogs broadcast sound without expelling air.
Air does not exit the mouth; rather, it cycles back and forth between the buccal cavity and lungs.
Generally used in breeding season , to call the female frogs
31 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
Cloaca:
The cloaca is a short tube that extends from its union with the caudal end of the large intestine to the exterior.
It is a common chamber that receives feces, urine, and gametes and releases them to the exterior through the cloacal aperture.
Male cloaca serves as a temporary reservoir for sperm prior to fertilization.
Female cloaca is as a temporary storage site for eggs as they pass between the uterus and the exterior.
Answer the Following (8 Marks)
Q.20. Describe the External Features of Frog.
Ans:
1) Shape and Colour:
Body of frog is spindle – shaped, pointed anteriorly and rounded posteriorly.
It is slightly flattened dorsoventrally and streamlined to swim through water.
They body of frog is divisible into head, trunk and limbs.
32 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Size of adult Rana tigrina varies from 12 to 18 cm in length and 5 to 8 cm in width.
2) Skin and colour:
Skin of Frog is thin, moist slimy, smooth and fitting loosely on the body.
Skin of back has dorso- lateral folds or thickenings called dermal plicae.
Colour of skin is green with black or brown spots dorsally but lighter pale – yellow ventrally.
A light yellow mid – dorsal line runs from tip of snout to the cloacal opening on the back.
3) Head:
Head of the frog is flat , roughly triangular in outline and with a short blunt anterior snout terminating in a wide transverse mouth.
Two small opening, the external nares or external nostrils, lie dorsally above the mouth , it serves in respiration.
Two very large, spherical and protruding eyes are situated dorsolaterally on top of head.
The eyes have to eyelids, upper eyelid and lower eyelid.
Behind and below each eye is a conspicuous, flat and deeply pigments circular patch of skin, the eardrum or tympanum that receives sound waves. External ears are lacking.
The throat bears two bluish patches of skin , the vocal sacs, which helps in intensifying sound of croaking . 33 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
4) Trunk:
Head is broadly joined behind with the flat ovoid trunk.
Its back is raised in the middle in a characteristics sacral prominence of hump.
At the posterior end of trunk is a small circular cloacal aperture or vent for the discharge of faecal and urinary wastes as well as reproductive products.
5) Limbs:
Laterally, the trunk bears two pairs of limbs or appendages.
The short forelimbs arise anteriorly from trunk just behind the head.
Each forelimb consists of the upper arm (brachium) , forearm ( antebrachium), wrist ( carpus) and hand ( manus) bearing four digits without web.
Thumb or pollex is vestigial.
The much elongated and powerful hind limbs or legs arise close together posteriorly from trunk.
Each hind limbs consist of thigh, shank( crus), much legthened ankle ( larsus) and large foot ( pes) having five slender clawless toes connected by broad thin webs of skin.
34 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
External Features of Frog
Q.21. Describe the digestive system of frog
Ans:
Digestive system of frog includes the digestive tract or alimentary canal and the associated digestive glands.
1) Alimentary canal:
35 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Alimentary canal of frog is a long and coiled tube of varying diameter extending between mouth and cloaca.
It consists of buccal cavity , pharynx, Oesophagus , stomach , small intestine , large intestine and cloaca.
(i)Mouth:
Alimentary canal begins at the mouth opening.
It is a wide gap, extending from one side of the snout to the other.
It is bounded by two bony jaws covered by immovable lips.
Upper jaw is fixed while the lower jaw can move up and down to close or open the mouth.
(ii)Buccal Cavity:
Mouth opens into a large, wide and shallow oral or buccal cavity.
Its ciliated columnar epithelial lining contains mucous glands which secretes mucus for lubricating food.
There are no salivary glands in frog.
(a)Teeth:
The lower jaw lacks the teeth, but small conical and backwardly pointed teeth occur in a row on either side on the premaxillae and maxillae bones of the upper jaw.
Teeth are not meant for chewing; they just hold the prey in their mouth and prevent it from escaping.
36 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Teeth are similar, not set in a socket, but each attached to the jaw bone.
In life, teeth of frog are replaced several times by the growth of new teeth when worn out or lost.
(b)Tongue:
On the floor of mouth cavity lies a large, muscular sticky protrusible tongue.
Its anterior end is attached end is attached to the inner border of lower jaw.
Its posterior end is free and bifid which can be flicked out and retracted suddenly after capturing the prey with its slimy surface.
(c)Internal nostrils:
The roof of buccal cavity contains anteriorly, a pair of small openings of internal nares, by which the nasal cavities open into buccal cavity.
These helps in respiration.
(d)Bulgings of orbits:
The roof of buccal shows two large oval and pale areas, the bulging of eyeballs while swallowing food, frog depresses the eyes causing the orbits to bulge inward and push the food towards the pharynx.
3) Pharynx:
Posteriorly, the buccal cavity passes without demarcation into a short pharynx.
A median elevation on the floor carries a longitudinal slit- like aperture, the glottis, leading into the laryngo-tracheal chamber.
37 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology In the roof on either lateral side is a wide eustachian aperture which opens into the middle ear.
4) Oesophagus:
Oesophagus is a short, wide muscular and highly distensible tube.
It contains mucous glands.
Longitudinal folding of the oesophagus allows its expansion during the passage of food into the stomach.
5) Stomach:
Stomach lies on the left side in the body cavity, attached to the dorsal body wall by a mesentery called mesogaster.
It is a large, broad and slightly curved bag or tube with thick muscular walls.
Its large broader anterior part is called as cardiac stomach, while the short narrower posterior part is called as pyloric stomach.
The inner surface of the stomach has several prominent longitudinal folds which allow its distension when food is received.
Its mucous epithelium contains multicellular gastric gland, secreting the enzymes pepsinogen, and unicellular oxyntic glands, secreting hydrochloric acid.
The posterior or pyloric end of stomach is slightly constricted and opens into small intestine.
Stomach serves for storage and digestion of food.
38 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology 6) Small intestine:
Small intestine is a long, coiled and narrow tube, attached mid- dorsally to body wall.
It is made up of two parts (a) a small anterior duodenum and (b) longer posterior ileum.
(a) Duodenum:
It runs a head parallel to stomach forming a U shape.
It receives a common hepatopancreatic duct from liver and pancreas bringing bile and pancreatic juice.
(b)Ileum:
It is the longest part of the alimentary canal and makes several loops before enlarging posteriorly to join rectum.
Digestion of food and absorption of digested food occur in the small intestine.
7) Large intestine or rectum:
It is a short, wide tube running straight behind to open into cloaca by anus.
Its function is the re- absorption of water and the preparation and storage of faeces.
8) Cloaca:
It is the small terminal sac-like part which opens the anus and the urinogenital apertures.
39 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Cloaca opens to outside by the vent or cloacal aperture, lying at the hind of the body.
Digestive System of Frog
40 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
Q.22. Discuss the Male reproductive system of frog
Ans:
Male reproductive of frog consists of two testes attached to kidneys , several vasa efferentia and two urinogenital ducts.
Copulatory organs are lacking
1) Testes :
A testis is an elongated or ovoid, light –yellow body attached to the antero- ventral surface of each kidney by a double fold of peritoneum called mesorchium.
Near the anterior end of the testis, several branched finger-like fat bodies arise which provide reserve food used to nourish developing spermatozoa and during hibernation.
Each testis is a compact mass of much coiled seminiferous tubules, the epithelial lining of which produces spermatozoa by spermatogenesis.
A mature sperm is elongated structure.
It consist of a small rounded anterior acrosome, a long cylindrical head containing nucleus , a short middle piece containing centrioles and mitochondria and a much elongated posterior motile tail terminating in a flagellum.
41 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
2) Vasa efferentia:
All the seminiferous tubules in a testes are connected to form 10 to 12 narrow tubes, the vasa efferentia.
These leave from the inner margin of testis, run through mesorchium and enter the inner margin of the kidney to open into the Bidder’s canal.
The Bidder’s canal is then connected to the ureter through collecting tubules of kidney.
Thus vasa efferentia conduct mature spermatozoa from testis to the ureter of kidney.
3) Urinogenital duct:
As ureter in male frog is both a urinary duct and a vas deferens, hence it is called a urinogenital duct.
The ducts of both the sides open into roof of cloaca separately on urinogenital papillae.
In some species of frog, the urinogenital ducts are enlarged near kidneys or cloaca forming seminal vesicles for temporary storage of spermatozoa until needed.
42 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
Mature sperm of Frog
Q.23. Describe the Female Reproductive system in frog
Ans:
43 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Female reproductive system of frog consist of two ovaries and two oviducts
1) Ovaries:
Each ovary is attached to the dorsal abdominal wall, near kidney, supported by a peritoneal fold called mesovarium.
It is a large, irregularly folded, multilobed, hollow sac grayish or blackish in colour.
In breeding season, the two ovaries become greatly enlarged.
Each ovary contains innumerable dark round ova in different stages of development.
Ova arise from germinal epithelial lining by oogenesis.
When ripe the ova are shed by rupture of ovarian wall into the body cavity from there are moved by cilia of peritoneum into the ostia of oviducts.
2) Oviducts:
The two oviducts are long and much coiled white glandular tubes not connected directly to the ovaries.
Their anterior ends form ciliated funnel – like opening, the Ostia.
These are placed anteriorly in the body cavity at the base of the lungs one on either side of oesophagus.
Cilia present on the inner wall of oviducts move the eggs posteriorly while glands secrete an albuminous coat around each egg during its passage.
44 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology The posterior ends of oviducts open dorsally into cloaca separately on papillae just in front of the ureters.
Just before entering cloaca, each oviduct forms a thin – walled enlargement, the ovisac.
The eggs are collected inside the ovisac before being laid.
An unfertilized ripe egg of a frog is spherical with a nucleus.
It contains a yolk called as vegetal hemisphere or pole.
Egg of frog is telolecithal and radially symmetrical.
Around the egg is a two-layered vitelline membrane of its own secretion.
The outer aluminous coat on contact with water swells into a thick jelly like layer which probably prevents overcrowding and protects from infections and predators.
45 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
Q.24. Describe the Central Nervous System of frog. (April -2011)
Ans:
The nervous system of frog is composed of 3 main sub- divisions.
A) Central nervous system consisting of brain and spinal cord.
B) Peripheral nervous system consisting of cranial and spinal nerves.
C) Sympathetic nervous system consisting of sympathetic nerves and ganglia.
A) Central nervous system.
1) Brain:
46 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Brain is a white coloured , elongated and somewhat flattened structure , lying well protected inside the cranium of skull.
It is surrounded by two connective tissue membranes, called meninges.
The inner or piamater is delicate, pigmented, vascular and closely applied to brain.
The outer durameter is tough, fibrous and lines the cranial cavity.
The narrow space between the membranes and the inner cavities of brain are filled with a clear, watery and lymphatic cerebro-spinal fluid which protects and nourishes brain.
The inner cavities of brain, called ventricles are continuous with one another.
Brain has well developed cerebrum and optic lobes.
Brain is further divided into 3 main parts.
i) Forebrain: It includes two olfactory lobes, two cerebral hemisphere and a diencephalon.
(a)Olfactory lobes:
There are two anterior most, small and spherical lobes each sending a small olfactory nerve to the nasal chamber of its side.
The two lobes are united but each contains a separate small cavity, the olfactory ventricle or rhinocoel.
Olfactory lobes are concerned with sense of smell which is poor in frog.
(b)Cerebral hemisphere: 47 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Posteriorly , the olfactory lobes are isolated by a slight constriction from two large cerebral hemisphere forming the cerebrum.
These are long, oval and smooth structures, narrow in front but broad behind.
Separated from one another by a deep mid-longitudinal groove or fissure.
The large cavities of hemisphere called I, II or lateral ventricles or paracoels, are continuous anteriorly with the olfactory ventricles.
Posteriorly they unite with each other and with the III ventricle or diocoel of dienceohalon through a common opening called foramen of Monro.
Thin roof of cerebrum is called pallium but each ventro- lateral side is thick , called corpus striatum which is made up of white medullated nerve fibres and cells.
The two corpus striata are joined together by a transverse fibrous tract, the anterior commissure.
The hemisphere is the seat of memory, intelligence, consciousness and will, and regulate voluntary actions.
(c)Diencephalon:
It is the short, rhomboid, depressed region just behind the cerebrum.
Its small cavity, III ventricle or dioceol, has thick lateral walls called optic thalamic and a thick floor, called hypothalamus.
Its dorsal roof contains a network of blood capillaries, called anterior choroid plexus, behind which arises a small hollow projection, the pineal stalk that runs to the brow spot.
48 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology In tadpole a small spherical pineal body is attached to the stalk.
But, it is detached and comes to lie outside skull in adult frog.
Ventral surface of dincephalon bears the X- shaped optic chiasma formed by the two optic nerves crossing each other.
Just posterior to optic chiasma is a large median bilobed projection, the infundibulum, which bears a flattened oval pituitary body or hypophysis.
Diencephalon is concerned with vision and balance. ii) Midbrain:
It is the broadest part of the brain containing a narrow canal, the iter or aqueduct of Sylvius, which is continuous with III ventricle in front and IV ventricle behind.
Midbrain bears dorso-laterally two large rounded optic lobes , called corpora bigemina.
Their canals called optocoels, open into iter.
Two thick longitudinal bands of nerve fibres , called crura cerebri, run longitudinally beneath optic lobes connecting diencephalon and medulla .
The optic lobes inhibit spinal cord reflexes, and each controls the opposite side of body.
iii) Hindbrain:
The posterior part of brain includes cerebellum and medulla oblongata.
(a) Cerebellum: 49 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology It is poorly developed narrow transverse solid ridge or band, placed dorsally behind the optic lobes.
It controls equilibrium and muscular coordination which are of little importance in frog.
(b) Medulla oblongata:
It is the last small conical part which is continuous with spinal cord without distinction.
Its triangular cavity, called IV ventricle or metacoel, is continuous anteriorly with iter and posteriorly with the central cavity of spinal cord.
The thin and highly vascular dorsal roof of metacoel forms the posterior choroid plexus.
Medulla controls important involuntary functions such as heart beat, metabolism, respiration, etc.
2) Spinal Cord:
The spinal cord extends posteriorly from medulla oblongata through foramen magnum and lies protected within the neural canal of vertebral column.
It is a short, thick, cylindrical, somewhat flattened and white in colour .
Like brain, spinal cord is also surrounded by the two meninges, piamater and durameter, containing protective and nourishing cerebro-spinal fluid.
Posteriorly it terminates into a fine , non- nervous filament , filum terminale, in the urostyle .
50 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Spinal cord shows swelling in two places – brachial enlargement between forelimbs and sciatic or lumbar swelling anterior to filum terminale .
Throughout its length run two longitudinal grooves, the mid- dorsal called dorsal fissure and the mid- ventral called ventral fissure.
It encloses a narrow central canal which is a continuation of the ventricles of brain.
Spinal cord is made up of outer white matter composed of nerve fibres and inner grey matter, largely of nerve cells.
Spinal cord is mainly concerned with the reflex action.
Frog structure of Brain A- Dorsal View , B- Ventral View, C- Longitudinal horizontal section showing Ventricles. 51 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
Q.25. Discuss the structure and working of heart in frog.
Ans:
Frog has a closed circulatory system.
It includes heart, arterial system, venous system and blood.
Its chief function is to transport all necessary liquids and gaseous material to the living tissues and to bring away from them the liquid and gaseous wastes of metabolism to organ of elimination.
1) Heart:
The muscular heart is the central pumping station driving blood through the closed circulatory system. i) External features:
The heart lies mid- ventrally inside the anterior trunk region protected by the pectoral girdle .
It is reddish in colour and somewhat conical or triangular in shape with the broad base directed anteriorly and the narrow apex, posteriorly.
(a) Pericardium:
The heart lies enclosed by a thin, transparent, two – layered sac, the pericardium.
Then outer wall of pericardium, parietal pericardium and inner wall of which closely invests the heart, called visceral pericardium.
52 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology The narrow cavity between two pericardial layers contains a watery pericardial fluid which protects the heart from friction or mechanical shocks. Keeps it moist and permits its movement.
(b) Chambers of heart:
Frog’s heart is a three chambered structures, made up of two anterior dark- coloured atria or auricles, right and left, and a single posterior conical and pink- coloured ventricle.
The two auricles are externally isolated by a very faint longitudinal inter- auricular groove.
The two auricles are clearly marked off- from ventricles by a narrow transverse auriculo-ventricular groove or coronary sulcus.
Additional two chambers of heart are sinus venous and truncus arteriosus.
Sinus venosus is a dark – coloured , thin walled and triangular chamber attached dorsally to heart.
Truncus arteriosus arising anteriorly from the right ventral side of ventricle, it is a tubular chamber.
It bifurcates anteriorly into two branches or trunks , each further breaks into three arches carotid, systemic and pulmocutaneous.
53 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
ii) Internal Features:
The internal structure of heart is hollow and muscular .
The various chambers are separated by valves to keep the blood flow in one direction.
(a)Auricles:
The two auricles, right and left are thin –walled and completely separated from each other by a thin vertical inter-auricular septum.
Right auricle is larger than the left one .
Sinus venous opens into dorsal wall of right auricle through a large transverse oval aperture.
The pulmonary vein opens into left auricle , near septum by a small opening without valves.
54 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Both auricles open into single ventricle by a common large auriculo-ventricular aperture guarded by two pairs of flap –like ventricular valves.
(b) Ventricle:
The ventricle has thick muscular and spongy wall.
Its inner surface has irregular strands or ridges, the columnae carneae or trabeculae, with depressions called fissures.
The flaps of auriculo-ventricular valves are connected to the wall of ventricle by thread –like chordate tendineae.
(c) Truncus arteriosus:
The opening of ventricle into truncus arteriosus is guarded by 3 semilunar valves,which prevents back flow of blood from truncus into ventricle.
The spirally twisted cavity of trunncus arteriosus is divided unequally by another set of 3 semilunar valves into a long basal thick walled conus arteriosus or pylangium and a short distal thin – walled bulbous aorta or synangium.
A large twisted longitudinal spiral valves further divides the cavity of conus or pylangium into a left dorsal cavum pulmocutaneum and a right ventral cavum aorticum.
The spiral valve is attached dorsally while its ventral edge is free.
The common opening of the two pulmocutaneous arches lies in cavum pulmocutaneous , while separate openings of carotid and systematic arhes lie in synangium.
All these opening are guarded by valves.
55 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology The distal right and left branches or trunks appear externally to be single vessels but internally, each is made of 3 channesl which eventually form three separate arches on either side.
Working of heart:
Heart beats continuously during life.
Contraction of heart is called systole, while its relaxation is called diastole.
Different chambers of heart contract in a regular sequence and the valves present , prevent the back flow of blood.
When the sinus venosus contracts, its nonoxygenated venous blood is forced into the right auricle through sinuauricular aperture. 56 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology While the oxygenated blood from the lungs is poured into left auricle through common pulmonary vein.
The two auricles now contract almost simultaneously forcing their blood into ventricle through the single auriculo-ventricular aperture.
Q.26. Discuss the Arterial system in frog.
Ans:
Aortic arches:
Arteries carry blood away from the heart.
The arterial system in frog begins with the truncus arteriosus.
Truncus arteriosus arteries is further divided into three major vessels
Called (i) Common carotid to head, (ii) systemic to body and viscera, and (iii) pulmocutaneous to lung and skin.
1)Common carotid arch :
It is a short vessel running forward and outward.
It further divides into external and internal carotids
(a)External carotid: 57 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Also called lingual , it is the smaller inner branch carrying blood to the tongue and adjacent parts.
(b) Internal carotid:
It is the larger outer branch.
At its base its forms a little swelling, the carotid labyrinth or gland.
Its lumen is converted into a labyrinth by folding of the wall.
The inner cavity of carotid labyrinth contains a network of small vessels and forms a spongy structure.
It is probably a sense organ and controls blood pressure.
The internal carotid divides into 3- branches – a palatine to the roof of mouth, a cerebral to the brain, and an ophthalmic to the eye.
2) Systemic arch.
It is the longest of the three arches and with greatest distribution of blood.
The two systemic arches curve dorsally around the oesophagus and join with each other behind the heart to form the dorsal aorta.
It divides into three arteries.
(a) Oesophageal: A small artery to oesophagus . It may arise from occipito- vertebral.
(b) Occipito-vertebral: It sends an occipital branch to occiput or posterior part of head, and a vertebral branch to vertebral column and spinal cord. 58 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology (c) Subclavian: It is a large artery supplying the shoulder region and extending into the forelimbs as branchial artery.
Dorsal aorta:
It is formed by the union of both the systemic arches.
It runs posteriorly lying mid-dorsally, beneath the vertebral column
It gives off the following arteries.
(a) Coeliaco-mesenteric:
It is a single large artery, arising from the junction of the two systemic arches.
It has two main branches: The coeliac to stomach, pancreas and liver; and the anterior mesenteric to spleen and intestine.
(b)Gonadial: A pair of short arteries to gonads, called spermatic in male and ovarian in female frog.
(c) Renal: While passing between the two kidneys, dorsal aorta sends off 5-6 pairs of small renal arteries in a series into both the kidneys.
(d) Posterior mesenteric: It arises from the posterior end of dorsal aorta , or sometimes from anterior mesenteric .It goes to large intestine or rectum.
(e)Common iliacs: The dorsal aorta bifurcates posteriorly into two common iliacs , each supplying an epigastric to ventral body wall , recto-vesicular to rectum and urinary bladder, femoral to hip and upper thigh , and sciatic to lower leg.
3) Pulmocutaneous arch:
59 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology It divided into two main arteries, pulmonary to the lung and cutaneous to skin of dorsal and lateral sides and various other structures .
Of these auricularis supply blood to tympanum, thymus gland, lower jaw, pharynx and hyoid etc.
While dorsalis supplies the skin of dorsal side and lateralis supplies the skin of lateral sides of the body.
60 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
61 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology Arterial system in Frog
Q.27. Discuss the Venous system in frog
Ans:
The venous system includes veins or those blood vessels in which blood of body returns to the heart.
In frog it can be studied in four parts:
1) Pulmonary veins 2) caval veins 3) renal portal veins and 4)hepatic portal veins
1) Pulmonary veins:
Oxygenated blood from two lungs is collected by right and left pulmonary veins which unite to form a common pulmonary vein opening directly into the left auricle on the dorsal side.
2)Caval veins:
Deoxygenated blood from rest of the body travels towards heart in three large vessels , two anterior venae cavae and single posterior vena cava , all the three opening into sinus venosus.
(a)Anterior Venae cavae or precavals:
The right and left precavals or anterior venae cavae collect venous blood from the anterior part of body.
Each precaval is formed by the union of 3 major veins which meet simultaneously
62 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology (i) External jugular: It is formed by the slender and sinuous lingual from tongue and mandibular from outer margin of lower jaw.
(ii)Innominate: It is formed by the internal jugular from cranial cavity and orbit and subscapular from shoulder and back of arm.
(iii) Subclavian : It is formed by the brachial from forelimb and the musculo- cutaneous from side of the body and head.
(b)Posterior vena cava or postcaval:
The single postcaval is large, dark-coloured vein, lying ventral to dorsal aorta.
Its posterior end is formed between the two kidneys from which it drains blood by 5-6 pairs of renal veins.
It also receives a pair of genital veins from gonads directly or through anterior pair of renal veins.
The postcaval then runs forwards , dorsally to the liver and receiving from it a pair of short , stout hepatic veins , before opening into the posterior angle of sinus venous.
3)Renal portal system:
Frog has two well developed portal systems, renal portal and hepatic , which are interconnected.
The veins which carry blood to a capillary system in kidneys constitutes the renal portal system.
Blood of each hind leg is collected by two veins, an outer fermoral and an inner sciatic.
63 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology On entering the abdominal cavity the femoral divides into a dorsal renal portal and ventral pelvic vein.
The renal postal unites with the sciatic of its side and while running along there outer border of kidney of its side it receives alone from lumbar region by a dorso- lumbar vein.
Renal postal vein enters the kidney by several branches which break up into capillaries.
4) Hepatic portal system:
A large hepatic portal vein is formed by the confluence of several branches from stomach , intestine, spleen and pancreas.
It carries blood of alimentary canal ‘laden with the digested foodstuff to liver where it breaks up into capillaries.
the pelvic veins of both sides unite to form a median ventral or anterior abdominal vein.
It receives blood form urinary bladder and ventral abdominal wall and runs forwards to enter liver into which it breaks up into capillaries.
Before entering liver the anterior abdominal and hepatic postal veins are connected by small loop.
64 Sharp’s Notes FY.Bsc. Paper I / Term II Zoology
Venous system of frog
65 Sharp’s Notes