609 



XIII. On the Homologies of certain Muscles connected with the Shoulder -joint. By 



George Rolleston, M.D., F.B.S., RES., Liuacre Professor of Anatomy 



Physiology, Oxford 



ml 



(Plate XLVII.) 



Eead June 14th, 1868. 



■J-HE main points of the paper which I have herewith the honour of laying before the 

 Linnean Society are, first, that the pcctoralis secundus s. levator humeri of birds finds 

 its homologue in the subclavius of mammals, and not in the pectoralis minor of anthro- 



potomy, and, secondly, that the " epicoraco-humeral" muscle, as described by Mr 



Mivart in the Echidna hystrix and in the Iguana tuberculata, is the honiologue 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 appo- 

 sition to its head, from the cartilage of the first rib, of fibres from the presternum 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 pectoral muscles. Of the four figures which accompany this paper, the first 

 two represent the bony structures of the shoulder- girdle of the Crocodile, and the cora- 

 co-scapular bone of the Emu ; whilst the third and fourth represent certain of the 

 muscles arising from these bones and passing to the upper extremity in either case. 

 Dissections from these two animals have been chosen for figuring, amongst other reasons, 



because the structural arrangements of the classes to which they respectively belong 

 express, as has been remarked by anatomists from the time of Meckel (' Vergleichcnde 

 Anatomic*, vol. iii. p. 194) to that of Mr. Parker (< Shoulder-Girdle,' 1808, pp. 112, 192), 

 certain of the problems of morphology in plainer language than those of most other 

 animals. It was whilst dissecting these and other animals in the light furnished me by 

 Mr. Mivart's papers on the myology of the Echidna hystrix (Trans. Linn. Soc. xxv. 

 1806) and the Iguana (Proc. Zool. Soc. June 27, 1807) l that I came to entertain the 



1 In the former of these two papers (at p. 395) a very extensive, if not exhaustive, bibliography was given of the 

 many disquisitions which had previously appeared on the subject of the Homology of the limbs and their muscles. 



followin 



in date to his paper. 



Hermann PfeifFer. Zur vergleichenden Anatomie des Schultergerustee 



Professor Haughton. " On the Muscular Anatomy of the Crocodile," 



June 26, 1865 ; Ann. and Mag. of Nat. Hist. Ser. iv. No. 4, April 1868. 



Giessen, 1854. 



Royal 



blister. " On Irregularity in the Muscles of the Shoulder," and " On the Homologies of the Flexor 



4P2 



