MUSCLES CONNECTED WITH fHB SHOULDER- JOINT. 6U 



from the tendon of the rectus abdominis as it passes upwards to be inserted into the manu- 



d first rib 



The muscle is folded upon itself much as the pectoralis major 



the human subject ; the concavity of the pouch thus formed looks inwards. 1 

 superficial portion of the muscle passes upwards; and its tendon Bpreads into the fascia 

 covering the supraspinal us, and thus is inserted into the acromion at it root, whilst 

 towards its apex, by the intermediation of fascia covering the acromion, it can act upon 



the fibres of the deltoid taking origin there. The portion of the muscle which lies 



deeper or more dorsally is inserted into the oorac id, into and along the eoraco-acromial 

 ligament, into a detached ossicle, which lies outside the anerle formed bv the mectinir of 

 acromion and clavicle, and finally into the clavicle. J hit the clavicle seems to give libr s 

 to the subclavius, as well as to receive the insertion of fibres from it; these fibres, how- 



ever, are but few in number, and seem to lie between the superficial and the deep port ion- 

 of the muscle. 



The subclaims of certain New-AYorld Monkeys (Mt/cetes senieulus and Mi/cetes Geoffiroyi) 

 furnish us with a stepping-stone whereby to pass from the tubcUwtiu of the three 



mammals just treated of to the subclarius of anthropotomy. In these Monkeys the sub- 

 clavius takes origin from the junction of the first costal cartilage, not with the sternum, 

 but with the rib, and it is inserted into the outer and under surface of the cla\ tele and 

 into the coracoid. But it has no origin from tin; 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 Canzor (cited by Mr. 

 Macalister, Cambridge Journal of Anatomy, May 1SG7, p. '518) as passin 

 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 eo, figured from the Crocodile in fig. 3, appended 

 to this paper, takes origin higher than the external oblique does ordinarily . 



I may now pass by a natural transition to a vindication of my proposition, that tli« 

 pectoralis secundus or levator humeri of the bird docs not find its homologue in the pee- 



■^ 



mm 



of the mammal. For the establishment of this negative proposition 



not sufficient to say that in each of the mammals from dissections of which I hav< 

 described a subclavius apparently homologous in origin, course, and insertion with th< 

 avian pectoralis secundus a muscle homologous with the human pectoralis \ nor is also 

 found, and that this coexist nee disprove- the view which as rts these two perforates to 

 be homologous; for the pectoralis minor may be muitiiid, 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, corner, either directly or through the intermediation of th 



* 



-> 



supraspinatus (which these fibres join), to act as an elevator of the humerus (see .Maca- 

 lister, Proceedings Royal Irish Academy, Pec. 1867; Cambridge Journal, May 1867, 

 p. 317; Wood, Proceedings Royal Society, May lb(>7, p. 52 1, June I860, p. 231); and 

 it is plain a priori that for the formation of an avian pectoralis secundus by the pectora lis 

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



