FORAMINA, FOSSA AND VACUITIES IN THE SKULL AND LOWER JAW OF MUD TURTLE, TRIONYX GANGETICUS (CUV.) BY D. K. MANSHARAMANI (Department of Zoology, ttolkar Science College, lndore) Received March 3, 1965 (Communicated by Dr. Benicharan Mahendra, F.A.SC.) As far as the author is aware, no work has been done on the skull of mud turtles specially the foramina, fossa and vacuities. I have therefore studied the cranial peculiarities of Trionyx gangeticus, with special reference to foramina, fossa and vacuities of the skull and lower jaw. Trionyx gangeticus, a monotypic, trionychid testudine, exhibits many foramina, fossa and vacuities in its skull, which is typically akinetic moni- mostylic and anapsidian. The latter condition undergoes partial modifi- cation in the shape of temporal region which reveals emargination. The temporal arch is formed by jugal and quadratojugal. The orbits are close to the anterior half separated by prefrontal on the dorsal side. The anterior nares are near the tip of the snout, bounded by prcunaxilla below and prefrontal above. The skull is oblong-swollen, nose convex-arched, forehead convex, upper jaw'with broad flat rugose alveolar plate, which is narrow in front and wide behind. It has three long posterior processes formed by supra- occipital in the middle and squamosals on either side. The premaxilla is extremely small, unpaired and does not reach the nasal cavity or the vomer. The maxillaries are correspondingly enlarged surrounding the choanae, which are separated by narrow vomer. The palatines form a broad deep concavity which is joined behind by long basi-sphenoid, which separates the long pterygoids from each other. The quadrate is trumpet-shaped. The zygomatic arch is complete, and is formed by quadrato-jugal and the jugal, the latter joining the maxillary and post-orbital. The prefrontals are large; the nasals are absent. The lower jaw has a broad deeply concave alveolar edge, narrow in front and wide behind. The mandible is remarkable for the great develop- ment of coronoid process. ~ 195 196 O.K. MANSHARAMANI FORAMINA--FOSSA AND VACUITIES Anterior nasal fossa (Fig. 1).--It is a large depression on the ant~riomes!al dorsal region of the snout. It is roughly hexagonal bounded anteriorly by premaxilla, laterally and posteriorly by maxilla and mesially by prefrontal. The nasal is absent. During life it is covered over by a membrane with circular orifice, the external nare. Orbital fossa (Fig. 1).--The orbital fossa is quite large roughly oval, on the anteriolateral dorsal side of the skull. It is bounded anteriorly by prefrontal, laterally by maxilla, mesially by frontal and posteriorly by post- frontal. Posterolaterally the temporal process of the jugal, completes the boundary of the orbit, and separates the orbit from the posteriorly situated temporal fossa. ~a'F x. f~m. &0. /'r.o r Flo. 1. Dorsal view (Natural size) of Tdonyx gangetleus. Temporal fossa (Fig. 1).--These are large vacuities, bounded anteriorly by post-frontal, mesially by parietal, laterally by jugal and quadrato-jugal and postoriorly by pro-otic. Foramina, Fossa and Vacuities in Skull and Power Jaw of Mud Turtle 197 Pathetic or trochelarforamen.--It is a pinpoint foramen in the anterio- lateral side of the cranium below the post-frontal for the passage of pathetic nerve to the superior oblique muscles of the eye in the living animal. Pro-otic foramen (Fig. 1).--On the dorsal side behind the temporal fossa deep in the pro-eric bone is the pro-otic foramen directed anteriorly and coming out of the cranial cavity. Foramen alveolaris superior (Fig. 2).men the lateral side of the skull the maxilla has a number of small foramina, known as foramina alveolare superior for the exit of cutaneous branches of the superior alveolar nerve of the maxillary branch of the trigeminal nerve proceeding to the skin. Foramen nervi trigemini (Fig. 2).--In between the parietal on the dorsal side and palatine on the ventral side, there is on the lateral side of the cranium, foramen nervi trigemini also termed foramen ovale. A little behind this is foramen nervi abducentis also termed canalis nervi abducentis, for the abducens nerve innervating the muscles of the eye in the living animal. Incisura columella (Fig. 2).--It is a small foramen in the depression of the quadrate on the lateral side for access to the internal ear in the living animal. Foramen arteria facialia (Fig. 2).--It is a small foramen in between the quadrate-jugal and the quadrate in the posterolateral side of the skull for the passage of blood vessels to the skin of the snout. F. I~" //>'~ ~J~.~:...-.,... ,... ...... ~ .........~ / '<::---"vM'I / /i Nm\,, /I \ FIG. 2. Lateral view (Natural size) of Trionyx gangeticus. Jacobsen foramen (Fig. 3).--It, bc~ween the pre-maxilla and the vetoer on the ventral side there is an arrow-skaped uneven opening broad at the anterior end and narrow at the posterior end known as Jacobsen foramen, ~onnocting Jacobsen organ with thQ c~vity of the mouth in th0 livin~ animah, 198 D.K. MANSHARAMANI Foramen orbitonasale (Fig. 3).--Behind the Jacobsen foramen on the ventral side in between the maxilla and palatine is an oval opening known as Foramen orbitonasale, also termed Foramen paltino-nasale. Foramen palatinum posterious (Fig. 3).--In the basal plate of palatine on the posterior side is foramen palatinum posterious--a narrow opening also termed canalis palatinum major et minor, FI'¢ t: I. ~.o. '? / FXG. 3. Ventral view (Natural size) of skull of Trionyx gangeticus. Foramen posterior canalis carotici interni (Fig. 3).--On the ventral side of the skull at the base of the pterygoid, and near its junction with the quadrate is foramen posterior canalis carotici intemi a circular opening directed backward arising out of the cranial cavity. Auditus canalis stapedio temporalis (Fig. 4).---On the posterior side of the skull, below and behind foramen posterior canalis carotici interni at the tri-junction of pterygoid, exo-occipital and opisthotie, is a large opening like inverted small bracket, auditus canalis stapedio temporalis, also termed foramen earoticum externum. Foramenjugulare posterious (Fig. 4).--On either side of foramen magnum in .the centre of exo-occipital is a circular opening, foramen jugulare posterior coming out of the cranial cavity, ~lso termed !ncisivum jugularis posterior, Foramina, Fossa and Vacuities in Skull and Power Jaw of Mud Turtle 199 Foramen jugulare anterus (Fig. 4).~It is a small foramen on either side of occipital condyle in the steepness of foramina jugulare posteris, also termed as foramina vago accessorium, for the branches of hypoglossal nerve, in the living animal. Foramen magnum (Fig. 4).--On the posterior side of the skull between the supraoccipital on the dorsal side and occipital condyle on the ventral side, in between the exo-occipitals, is a broad opening Foramen magnum, a gateway to the cranial cavity, also termed foramen oceipilate. Foramen supra angulare (Fig. 5).~It is an oval-shaped opening on the dorsal side of the mandible, in the supra-angular bone for the entry of the mandibular branch of trigeminal. ~.gTg I a:t J.ll. Flo. 4. Skull posterior view (Natural size) of Trionyx gangetlcus. Foramen dentofacialia (Fig. 5).--Here are a number of small foramina on the lateral side of the dentary for the inferior alveolar branch of trige- minal, entering through the foramen supra-angulare and coming out through the foramen dentofaeialia to the skin of the mouth. ~L: y .',~-,~.-t.: :~ i..: . ...":..:..k ~ ~ ~ -- ~.a.f. FIos. 5 and 6. Posterior and lateral views (NatUral size) of Mandible of Trionyx gangeticus. DISCUSSION The author's search for an account of foramina of the skull of Chelonia did not reveal any authentic account of them. However, Parsons and 200 D.K. MANSHARAMANI William's (1961) morphological study of the Jurassic turtles proved of some help. In a comparison of the foramina of the skull of Trionyx gangeticus with those of the two categories of the Portland and Solhofen specimens the following features are noteworthy: The skull is oblong swollen convex and broad like that of Lissemys, Dogania and differs from Chitra and Pelochelys, in which they are long and narrow. The proboscis is equal in Trionyx, to the orbital fossae, unlike Chitra where it is longer than the orbit and in Pelochelys it is only half of the orbit. The skull of Trionyx manifests a grade of organisation--presence of various fossa-foramina and vacuities, and their modification from Jurassic forms, indicating variations, and it is difficult to assume, which of the modifications are specialized and which primitive. Recent a Trionyx gangeticus is, there are no special features which are not founu in older forms. Some characters which are found in Jurassic turtles, and which could be termed as primitive, are absent in the present form. In Trionyx gangeticus the splenial and fossa Meckali are absent in the. lower jaw. In Chelidae, however, the splenials are of moderate size. In Trionyx skull there are no nasals and the anterior nasal fossa is not divided by partition. The pterygoids have no projections in the anterior side which could be termed as epipterygoids though they are present in Cryptodires. Thus the skull of Trionyx in these respects possesses more speeialised features than the Jurassic turtles. However, foramina prepala- tinum which are present in the Jurrassic forms are absent in Trionyx. The orbital fossa is roughly oval in shape and it varies in different forms. It is bounded by post-frontal from behind instead of post-orbital as in Jurassic forms. The temporal fossa is bounded in Trionyx on the lateral side by juga and quadrato-jugal. This secondarily emarginated temporal region is unique in mud turtles, which are typically anapsidian.