The Clavicle Or Collar Bone Develops in the Membranous Tissues Deep To

SECTION II THE UPPER LIMB CHAPTER 3 INTRODUCTION the central axis of the respective limbs Man is a mammal of the Primate and are said to be pre-axial, whereas tlie Order. He is a biped and he walks erect. 5th finger and ulna, and the 5th toe and His upper limbs are free and are adapted fibula lie on the caudal or tail side of this to purposes of prehension and not of axis and are said to be post-axial. The locomotion like the forelimbs of the palms of the hands face each other, and quadruped. They articulate with the so do the soles of the feet. Even at birth trunk at one small joint, the stemo- a baby might clap the soles of its feet clavicular joint, of their respective sides. almost as readily as the palms of its They possess great range of movement. hands. On assuming the Anatomical Pos His lower limbs have no such freedom. ture {fig. 1), the upper and lower limbs They have to bear the weight of his undergo rotation but in opposite direc body when he walks, runs, jumps, and tions; the thumb by rotating laterally stands. Accordingly, they are united be brings the palm of the hand to the front, hind to the vertebral column at the whilst the big toe by rotating medially sacro-iliac joints, and in front to each brings the sole of the foot to the ground. other at the symphysis pubis. The se The thumb and forearm can voluntarily curity the lower limbs enjoy is in the be caused to rotate medially, as, for ex upper limbs sacrificed to mobility. ample, when you let the palm of the hand It is generally held that the upper and rest on the knee. In this position the lower limbs are serially homologous, the distal parts of the upper and lower limbs thumb corresponding to the big toe, the come to occupy equivalent positions, and radius to the tibia, the ulna to the fibula, it becomes apparent that the dorsum of and the humerus to the femur. The cor the hand corresponds to the dorsum of responding parts are shown in table 1, the foot, the back of the forearm to the on the next page. front of the leg, the elbow to the knee, The clavicle or collar bone develops in and the back of the arm to the front of the membranous tissues deep to the skin the thigh. and has a different morphological history Mooring Muscles {fig. 56). The upper from the pubic bone which develops in limb is moored to the head, neck and cartilage. Strictly speaking the clavicle trunk by muscles, which may be likened is not represented in the lower limb, nor to guy ropes. The chief are: Trapezius is the pubic bone in the upper limb. which pulls the limb upwards; the Latis- They have, however, somewhat analo simus Dorsi and Pectoralis Major which gous functions to perform. pull it downwards; the Serratus Anterior In prenatal life the thumb and the which pulls it forwards; and the Rhom radius, and the big toe and the tibia are boids which (with the Trapezius) pull it situated on the cranial or head side of backwards. 74 THE UPPER LIMB 75 TABLE 1 Upper limb Lower limb Pectoral fClavicle 1 Pelvic girdle \Scapula Ilium ^ with coracoid process lechium J B-rdle Arm or Humerus Femur Thigh Brachium Forearm or (Radius Tibia \ , Antebrachium \Ulna Fibula J Carpal bones Tarsal bones Metacarpal bones Metatarsal bones Phalanges Phalanges Hand - > Foot 1st or Proximal 1st or Proximal 2nd or Middle 2nd or Middle 3rd or Distal 3rd or Distal Lines of Force Transmission. The with the shallow glenoid cavity of the following fundamental points should be scapula. The overhanging coraco-acro- verified by reference to the skeleton and mial arch (i.e., acromion, coraco-acromial figure 57. ligament, and coracoid process) forms a The clavicle is a strut that thrusts the hood-like roof, which prevents upward scapula laterally and backwards. It does dislocation of the humcrus. The lower so through the medium of a strong liga end of the humerus articulates with the ment, the coraco-clavicular. If this liga ulna and the radius. ment holds the scapula (and the rest The ulna is enlarged above and taper of the limb with it) away from the ing below; the radius is tapering above median plane, its fibers should pass and enlarged below; and, the two are downward and medially; and they do. The clavicle has an enlarged medial end Trapcaius which articulates with a shallow socket formed by the sternum and 1st rib cartilage. A strong articular disc pre Trapeaius vents the clavicle from being driven or^d medially on to the sternum. This is in RKomboids virtue of its diagonal mode of attachment to the clavicle above and 1st rib cartilage Scrratus below. The lateral end of the clavicle Ar\t«rior is not enlarged; it does little more than make contact with the acromion, the coraco-clavicular ligament being the es sential l)ond of union between the clavicle Pectoroi,le£( Loi\sstm.us and tlie scapula. Dorsi At the shoulder joint the rounded head Fi(!. 56. The upjier limb is moored to the of tiie humcrus makes side to side contact body by muscles. 76 A METHOD OF ANATOMY united by a strong interosseous mem- an articular disc whicli binds the radius hrane. Clearly, at the elbow joint the to the ulna. ulma is more important than the radius; 1. An impact, the result of, saj', a fall on the palm of the outstretched hand, C oraco-clovicular is transmitted by the scaphoid and lunate lig. Clavicle bones to the radius. The radius tran.'^fcrs Acromiorv. ,v part of the force directly to the huineriis and part, via an interosseous mem1)rane, to the ulna. To effect this transference of force the fibers of tlie membrane ob viously must pass downwards and me dially from radius to ulna. Thence the force travels up the humerus fa) to the overhanging coraco-acromial arch against which the upper end of the hu merus abuts and (b) in part across the glenoid cavity to the neck of the scapula, and up the coracoid process. If the force is sufihcient to overcome the lower moor ing muscles, the acromion and coracoid are driven upwards and the strut (i.e., the clavicle) may snap. 2. When force is applied to the side of the upper end of the humerus, the coraco-clavicular ligament prevents the scapula from beingdriven medially. This •IrvtefossGouS m.Gmbratvc it does in virtue of the direction of its fibers, which obviously must pass infero- medially. Disc 3. The force of an impact on the acromion is transmitted along the entire length of the clavicle and may result in fracture of the clavicle or in dislocation ®A of the acromio-clavicular joint. Fig. 57. Scheme of skeleton of limb showing lines of force transmission and ligaments trans PECTORAL REGION AND AXILLA ferring force as the result of a fall (1) on the hand—interosseous membrane, (2) on the The axilla is the pyramidal space shoulder—coraco-clavicular ligament, and (3) above the arm pit. It has 4 walls, an on the acromion—articular disc. apex, and a base (/ip. 58). The anterior wallis fleshy and is formed by the Pecto- at the wrist joint the contrary is true. ralis Major and two muscles that lie The enlarged lower end of the radius ar behind it enclosed in a sheet of fascia, ticulates with two carpal bones, namely, called the clavipectoral fascia. [This wall the scaphoid and lunate; but the ulna is practically synonymous with the Pec is separated from the carpal bones by toral Region, which, however, includes .

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