MYOLOGY 151 



the absence of this item of the skeleton there necessarily 

 result modifications in the arrangement of the muscles of 

 this region, which we must at the very outset explain, before 

 undertaking the special study of the muscle which is the 

 subject of the present paragraph. 



Let us suppose, for the more definite arrangement of our 

 ideas, that the clavicle is altogether absent, although we 

 do find it in a rudimentary state in some animals and 

 completely developed in others (marmot, bat), and we will 

 proceed to indicate what this absence determines. 



The great pectoral muscle in man arises in part from the 

 clavicle ; this origin not being possible in animals which have 

 no clavicle, its attachments, as we have already seen, are 

 concentrated on the sternum. The trapezius in man similarly 

 arises in part from the clavicle ; for the reasons above indi- 

 cated its clavicular fasciculi cannot exist in distinct form in 

 the animals which have no clavicle. 



. The sterno-clcido mastoid, whose inferior attachments we 

 mentioned above, cannot have a clavicular portion. 



It is the same in the case of the deltoid, which, we know, 

 arises in part from the anterior bone of the shoulder. 



Of the four muscles which have partial clavicular origins 

 in man, two are known to us in connection with animals — 

 the great pectoral and the trapezius. What has become 

 of the other two, the sterno-cleido mastoid and the 

 deltoid ? 



It is this which we now proceed to investigate. After a 

 fashion simple enough, but which it is necessary to describe, 

 the clavicular fasciculi of the trapezius and the corresponding 

 fasciculi of the sterno-cleido mastoid are united the one 

 to the other ; the portion of the deltoid which in man 

 arises from the clavicle, by reason of the absence of this 

 latter, is also combined with the fleshy mass formed by 

 the preceding muscles. From this fusion results the 

 muscle known as the mastoido-humeral. This muscle, 

 which consists of a long fleshy band situated on the 

 lateral aspect of the neck, takes its origin, as a general 

 rule, from the posterior surface of the skull and the upper 

 part of the neck, from which it passes obliquely downwards 



