Comparative Myology of the Chimpanzee. 359 



The arm is raised from the side by the Deltoid, which is 

 extremely thick and powerful, as is required by the length 

 and weight of the limb ; there is also an additional infra- 

 spinous portion of this muscle arising from the fascia of 

 the Infraspinatus and from the lower third of the anterior 

 border of the scapula, which would better enable the Chim- 

 panzee to swing the arm backward. The Deltoid, Supra 

 and Infra-spinati, Teres minor, and Subscapularis are a 

 great protection to the joint. 



The humerus is depressed, or, the hand being fixed, the 

 body is raised by the Pecloralis major in front, the Latis- 

 simus dorsi behind, and the Teres major arising from the 

 lower half of the anterior border of the scapula between 

 them. The three are very thick and strong ; the sternal 

 portions of the Pectorales majores nearly touch on the 

 middle line, but there is no division between them and the 

 clavicular portions, though the fibres cross before their in- 

 sertion as in man. The tendons of these three muscles 

 pass round the inside of the humerus towards the upper 

 surface, so as by their contraction to throw the elbow out- 

 wards, and keep the thumb and radial side of the forearm 

 inward and upward, which is obviously the most advan- 

 tageous position. In the lower species the Dernio-hiwier- 

 alis, described above, acts as a second Latissimus dorsi, 

 though of course much more feebly. The scapular head 

 of the Triceps, though part of the extensor, is neverthe- 

 less, when acting alone or with the other flexors of the 

 humerus, a powerful aid in climbing, its extensor power 

 being counteracted by the flexors of the forearm, which 

 act at a greater mechanical advantage, so that it can then 

 act only as a flexor of the humerus. 



In man there is occasionally found as an anomaly, a mus- 

 cular slip on the inside of the arm, from the tendon of the 

 Latissimus dorsi to some part of the elbow ; in most of the 

 Quadrumana, and in very many other animals, this mus- 



