CONNECTED WITH THE SHOULDER- JOINT. 117 



a single one. The rectus abdominis is prolonged up to the first 

 rib, and is overlapped in the guinea-pig by a muscle homologous with 

 that figured at e o in fig. 3, of the crocodile's shoulder-joint muscles ; 

 but it does not give any tendinous or muscular factor to the sub- 

 clavius here, as it does in the wombat (Pkascolomys wombat). A 

 description of the arrangement of these parts in this latter animal 

 will be found in my description of fig. 3, which, though taken from 

 a dissection of a crocodile, makes the account of the structures, as 

 seen in the wombat, much more intelligible. Both descriptions 

 alike warn us not to lose sight of the possibility that the avian 

 levator humeri may have borrowed a factor from the anterior pro- 

 longation, over the sternum, of the rectus abdominis. The arrange- 

 ment of these selfsame structures in the aardvark (Orycteropus 

 capensis) enforces the same lesson. In this animal (a detailed 

 account of the myology of which, by J. C. Galton, Esq., appears in 

 the Linnean Society's 'Transactions,' vol. xxvi. p. $Ji) the subcla- 

 vius arises from the manubrium, from the cartilage of the first rib, 

 and from the tendon of the rectus abdominis as it passes upwards 

 to be inserted into the manubrium and first rib. The muscle is folded 

 upon itself much as the pectoralis major is in the human subject ; 

 the concavity of the pouch thus formed looks inwards. The inferior 

 or superficial portion of the muscle passes upwards ; and its tendon 

 spreads into the fascia covering the supraspinatus, and thus is in- 

 serted into the acromion at its 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 coracoid, into 

 and along the coraco-acromial ligament, into a detached ossicle, 

 which lies outside the angle formed by the meeting of acromion 

 and clavicle, and finally into the clavicle. But the clavicle seems 

 to give fibres to the subclavius, as well as to receive the insertion 

 of fibres from it ; these fibres, however, are but few in number, and 

 seem to lie between the superficial and the deep portions of the 

 muscle. 



The subclavius of certain New World monkeys (Mycetes seni- 

 culus and Mycetes geoffroyi) furnishes us with a stepping-stone 

 whereby to pass from the subclavius of the three mammals just 

 treated of to the subclavius of anthropotomy. In these monkeys the 

 subclavius takes origin from the junction of the first costal 



