70 Proceedings of the Royal Irish Academy. 



from the eleventh, twelfth, and thirteenth ribs, and from the lumbiir 

 fascia. 



Teres minor is inseparable posteriorly from infraspinatus. 



Pectoralis minor is not represented, but its absence is compensated 

 for by pectoralis major, which consists of three parts; the first of these 

 arises from the presternum, and is inserted into the pectoral ridge, 

 which occupies about the upper two-fifths of the humerus ; the highest 

 fibres of origin are the lowest fibres of insertion, and the whole hume- 

 ral attachment is about four times as long as the sternal ; the second, 

 or bicipital part, arising from half an inch of the sternum below the 

 last, runs parallel to it, and is inserted into the inner border of the 

 flexor of the forearm, opposite the level of the supracondyloid foramen; 

 the third segment, arising from the whole length of the sternum, is 

 composed of two laminae, the superior being inserted underneath the 

 attachment of the first part, and equalling it in length, the deeper layer 

 going to the outer part of the head of the humerus and to the capsule 

 of the shoulder joint, with the anterior thoracic nerve crossing its 

 upper border and distributed to its superior aspect. No trace of this 

 remarkable arrangement seems to exist, either in Bradypus or Arcto- 

 pithecus, for the great pectoral in both is merely bilaminar, not even 

 presenting the presterno-humeral slip, though in the latter genus the 

 deep lamina of the third part sends a slip to the capsule of the shoulder 

 joint. It will be interesting to know if the curious insertion of the 

 second part be constant in Choloepus; Professor Humphry was not able 

 to determine its arrangement in his specimen. 



Pectoralis quartus(brachio-lateralis, Professor Humphry) arises from 

 the eighth, ninth, tenth, and eleventh ribs, and is inserted into the 

 head of the humerus. 



Coracobrachialis presented both the long and short varieties, the 

 former arising from the coracoid process and being inserted into the in- 

 ner edge of the humerus, behind the supracondyloid nerve ; the latter, 

 with a similar origin, is inserted into the humerus, below and behind 

 the tendons of latissimus dorsi and teres major. Mr. Galton describes 

 it as being thin, cord-like, and of uniform size, but does not say to 

 which variety it belongs. 



Subclavius extended from the first rib to the inner border of the 

 sternal end of the clavicle and to the acromion process, as was also the 

 case in Mr. Galton's specimen. 



Deltoideus is divisible, as usual, into three parts: scapular, acro- 

 mial, and clavicular; the first and largest of these arises from the spine 

 of the scapula, and is inserted into the deltoidal crest on the humerus; 

 the second part arises from the acromion process and outer border of 

 the clavicle, and is inserted into the radius along with the superficial 

 part of the biceps; the third has a similar origin to the second, and is 

 inserted along with, but free from, the first. Here again we have a 

 considerable difference from the arrangement in Ai, where the muscle is 

 not tripartite at all, though in Arctopithecus it supplies an accessory 

 head to the biceps. 



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