118 ON THE HOMOLOGIES OF CERTAIN MUSCLES 



cartilage, not with the sternum, but with the rib, and it is inserted 

 into the outer and under surface of the clavicle and into the 

 coracoid. But it has no origin from the sternum, and no scapular 

 nor any humeral insertion, either direct or indirect. 



The human subclavius may have an insertion into the coracoid 

 (Wood, 'Proc. Royal Soc' June 1864, p. 300); but such an 

 aberrant slip as that recorded by Ganzer (cited by Mr. Macalister, 

 ' Journal of Anatomy,' May, 1867, p. 318) as passing in the human 

 subject ' from the cartilage of the first rib to the capsule of the 

 shoulder beneath the pectoralis minor' I should be inclined to look 

 upon as merely a part of the deeper layers of the pectoralis major, 

 which took origin as much higher than those layers do ordinarily 

 reach, as the slip of muscle e 0, figured from the crocodile in 

 Plate 3, fig. 3, takes origin higher than the external oblique 

 does ordinarily. 



I may now pass by a natural transition to a vindication of my 

 proposition, that the pectoralis secundus or levator humeri of the 

 bird does not find its homologue in the pectoralis minor of the 

 mammal. For the establishment of this negative proposition, it is 

 not sufficient to say that in each of the mammals (from dissections 

 of which I have described a subclavius apparently homologous in 

 origin, course, and insertion with the avian pectoralis secundus) 

 a muscle homologous with the human pectoralis minor is also 

 found, and that this coexistence disproves the view which asserts 

 these two pectorales to be homologous ; for the pectoralis minor may 

 be multifid, and many instances have been put on record in which 

 it forms a groove for a portion of its fibres in the coracoid, and 

 working in it as over a pulley, comes, either directly or through 

 the intermediation of the supraspinatus (which these fibres join), 

 to act as an elevator of the humerus (see Macalister, * Proceedings 

 Royal Irish Academy,' Dec. 1867; 'Journal of Anatomy,' May 

 1867, p. 317 ; Wood, ' Proceedings Royal Society,' May 1867, 

 p. 524, June 1866, p. 231); and it is plain a priori that for the 

 formation of an avian pectoralis secundus by the pectoralis minor, 

 and for the alteration of its functions from that of a depressor into 

 that of a levator humeri, all that is necessary is the provision for 

 its tendon of some such pulley-like arrangement by the coracoid. 

 What I have to show is that, as a matter of fact, the muscle which, 

 in the economy of nature, has been worked up into the avian 



