120 ON THE HOMOLOGIES OP CERTAIN MUSCLES 



insertion. The second shows that they are or are not supplied by 

 the same nerve or nerves. The third shows that either in their 

 adult condition or in the condition of development they are in- 

 dependent or connate. A comparison of the pectoralis minor of 

 the mammal with the pectoralis secundus of the bird furnishes us, 

 under each of these three heads, with an argument for their non- 

 identity. Under the first head I would observe, as Prof. Pagen- 

 stecher has already been quoted as doing, that the pectoralis minor 

 of the mammal lies to the outer side of the costocoracoid mem- 

 brane, to the inner side of the homological representative of which 

 structure, viz. the coracoid, the pectoralis secundus of the bird 

 passes. I do not mean to deny, nor yet to affirm, that the pecto- 

 ralis minor of the mammal may not be one of the same series of 

 muscular fasciculi as its subclavius ; what I do affirm is, that there 

 is a certain landmark between these two muscles enabling us to 

 separate them into two sets, and that there is a similar separation 

 recognisable in the bird, of similar muscles by means of a similar 

 landmark. Under the second head I shall show 7 that the sub- 

 clavius of the mammal is supplied by a nerve homologous with 

 the nerve which supplies the pectoralis secundus of the bird, and 

 that the pectoralis minor is not supplied by that nerve, but by the 

 same nerve as that which in the bird supplies the great pectoral. 

 And, thirdly, I shall show that in the developing bird it is possible 

 to see that the pectoralis major is really the equivalent of both 

 pectorals of the mammal. The facts of the anatomical arrange- 

 ments in any single bird will give my arguments in their most 

 intelligible form ; and I will proceed to give them in an account 

 of the structures in question, as seen in the common sparrow-hawk 

 (Accijoiter nisus). 



The pectoralis secundus s. levator humeri has a much smaller 

 area of origin from the sternum and its keel in the sparrow-hawk 

 (Accijoiter nisus) than in the common fowl. It receives, however, 

 an accession of fibres, first from the anterior inferior angle of the 

 coracoid, and secondly from a large head which, arising from the 

 posterior or upper surface of the coracoid groove in the sternum, 

 from the lateral aspect of the sternal rostrum, from the upper 

 surface of the inner angle of the coracoid itself, and, finally, from 

 the. upper surface of a fibrous band which passes from the posterior 

 lip of the coracoid groove in the sternum to fix itself to the 



