CONNECTED WITH THE SHOULDER-JOINT. 119 



levator humeri is one and not the other of two, either of which, so 

 far as we can see, might have been so employed. 



I cannot adopt Prof. Pagenstecher's views (' Zool. Gart.' April 

 1867, p. 125), according to which the two mammalian pectorales 

 are referred to two entirely distinct sets of muscles, the pectoralis 

 major being one of a ventral, and the pectoralis minor one of a 

 dorsal series. The single fact of their both receiving a nerve- 

 supply from the same nerve (the internal anterior thoracic) seems 

 to be conclusive against the validity of this suggestion. And I 

 believe further, that it is impossible to observe how the posterior 

 fascicles of the pectoralis major in the lower Mammalia have their 

 tendons prolonged up from the lesser tuberosity of the humerus 

 and the bicipital groove, which is bridged over by pectoral tendons, 

 to the coracoid process, without being convinced that the pectoralis 

 minor of anthropotomy is but a specialised anterior fascicle of the 

 deeper portions of the pectoralis major. The commonest variation, 

 according to Mr. Macalister (' Journal of Anatomy and Physiology,' 

 May 1867, p. 317), which the pectoralis minor exhibits in man 

 is an insertion of the lowest part of its tendon, missing as it were 

 the coracoid process, into the coraco-brachialis muscle. 



The arguments which I shall now adduce to show that the 

 pectoralis minor is not the homologue of the avian pectoralis 

 secundus will at the same time go some way towards proving that 

 the primary insertion of the mammalian muscle is a humeral one, 

 more or less internally to the tendon of the superficial layers of the 

 greater pectoral, whilst the primary insertion of the avian is also 

 a humeral one, but one more or less externally placed to that of the 

 great pectoral depressor of the humerus. The attachment of the 

 mammalian pectoral to the coracoid is secondary in its history; 

 and the like place in the series of its specialisations is held by the 

 development of the coracoid pulley in the history of the avian 

 pectoralis secundus. The insertion of the ' subclavius ' into the 

 clavicle and the junction of the 'pectoralis minor' with the 

 supraspinatus will be seen in the course of the argument to be 

 exclusively mammalian developments. Now there are three lines 

 of argument for showing the homological identity or non-identity 

 of any two muscles. The first line of argument shows that they 

 hold the same or different relations to the other structures they 

 are connected with at their origin, in their course, or at their 



