XL 



ON THE HOMOLOGIES OF CERTAIN MUSCLES 

 CONNECTED WITH THE SHOULDER-JOINT. 



The main points of the paper which I have herewith the honour 

 of laying before the Linnean Society are, first, that the pectoralis 

 secundus s. levator humeri of birds finds its homologue in the sub- 

 clavius of mammals, and not in the pectoralis minor of an thro - 

 potomy, and, secondly, that the ' epicoraco-humeral ' muscle, as 

 described by Mr. Mivart in the Echidna hystrix and in the Iguana 

 tuberculata, is the homologue of the two former of the three 

 muscles now mentioned. A minor issue will be raised as to the 

 source whence the sternal factor of the avian levator humeri comes 

 to be added to the reptilian epicoraco-humeral, which, as its name 

 implies, has no such mesial point of origin : and it may be stated 

 at once that, though the mammalian subclavius furnishes instances 

 of two methods whereby the subclavius of man may acquire such 

 an accessory point of origin, viz. either by borrowing from the 

 rectus abdominis, or by simple apposition to its head, from the 

 cartilage of the first rib, of fibres from the praesternum on which it 

 abuts ; the analogy of other animals seems to point to its being in 

 this latter way that this addition is made. Some other points of 

 less moment will arise in the discussion of these questions, or be 

 brought forward at the conclusion of the argument as to the pec- 

 toral muscles. Dissections of the bony structures of the shoulder- 

 girdle of the crocodile, and the coraco-scapular bone of the emu, 

 and of certain of the muscles arising from these bones and passing 

 to the upper extremity in either case, have been chosen for special 

 examination, amongst other reasons, because the structural arrange- 

 ments of the classes to which they respectively belong express, 

 as has been remarked by anatomists from the time of Meckel 

 (' Vergleichende Anatomie,' vol. iii. p. 194) to that of Mr. Parker 



