316 THE MUSCLES. 



nerves on the inner aspect of the arm. The anterior humeral nerve passes 

 between its two branches, along with an arterial and venous ramification. 



Action. — It is an adductor of the arm, and makes it also pivot inwards. Its 

 direction and attachments do not permit it to produce rotation outwards, though 

 it has been stated to do so by several authors. 



4. Small Scapulo-humeralis (Scapulo-humeralis Gracilis, vScapulo- 

 humeralis posticus). 



(Synonyms. — Not mentioned by Percivall. Leyh, in addition to the above designation, 

 names it the tensor of the capsular ligament.) 



The scapulo-humeralis gi-acilis is a very small cylindrical fasciculus, compiised 

 between the large extensor of the forearm and the capsule of the scapulo-humeral 

 articulation ; it derives its origin above the margin of the glenoid cavity of the 

 scapula, and tenninates below the head of the humerus by a thin tendon, which 

 insinuates itself between the fibres of the short flexor of the forearm. This 

 muscle appears to be peculiar to Solipeds, and has been regarded by Rigot as 

 intended to raise the capsule of the scapulo-humeral articulation during flexion, 

 so as to prevent its being pinched between the articular surfaces. 



Differential Charactebs in the Muscles of the Shoulder in the other Animals. 



The Carnivora are the only animals which oflPer somewhat notable differences in the 

 muscles of the shoulder. 



Thus, the long abductor of the arm, very developed, has an anterior portion arising directly 

 from the acromion process, and a posterior portion which springs from the whole extent of the 

 scapular spine, by a short aponeurosis. The supra- spinatus is considerable, and terminates in 

 a single branch that goes to the great trochanter. 



The infra- spinatus is not so large as the preceding, and is also undivided at its inferior 

 extremity : it is the inferior branch which is absent. 



The coraco-humeralis is very short, and is composed of a single fasciculus, which terminates 

 above the humeral insertion of the adductor of tlie arm. 



In the Pig, the disposition of this muscle is the same ; it is very tendinous. 



In the Camel, on the external surface of the scapular region is an elastic layer which 

 extends over all the limb, and is worthy of notice. It arises from the borders of the cervical 

 ligament, covers the shoulder and arm, and is thickest behind the scapulo-humeral angle, 

 where the abductors and extensors of the forearm separate. It descends on the forearm in 

 front of the humero-radial articulation, and reaches the lower third of the anterior face of that 

 region, where it divides into two portions. The narrower and thinner of these go to the front 

 of the knee, where it gradually disappears in becoming thinner and lighter-coloured; the 

 largest division passes behind, and joins an equally elastic layer which comes from the inner 

 surface of the olecranian muscles and the elbow ; it reaches behind the knee, where it divides 

 into several strips, some of which are fixed into the inner border of the carpus and metacarpus, 

 and others on the flexor tendons of the phalanges, behind the metacarpo-phalangeal articulations. 



This very remarkable elastic apparatus tends incessantly to flex the bone of the anterior 

 limb; and to its presence must certainly be attributed the characteristic locomotion of the 

 Camel — ^jerking and almost passive flexion of the metacarpus on the forearm, and the forearm 

 on the arm. 



In the Camel, it is also remarked that the long abductor of the arm is entirely muscular, and, 

 superiorly, is only attaclied to the acromion spine. 



Comparison of the Muscles of the Shoulder op Man with those of Animals. 



As muscles of the shoulder, there are only described the deltoid, infraspinatus, teres minor 

 and major, and the subscapularis ; the coraco-brachialis being included in the region of the 

 arm, while the small scapulo-humeralis is absent (see Fig. 180). 



The deltoid, represented in part by the long abductor of the arm of Solipeds, is a large, 

 triangular, flat muscle, that covers the articulation of the shoulder. Its fibres are inserted 

 into the external third of the anterior border of the clavicle, the external border of the aero- 



