MYOLOGY 59 



scapula. Many of its fibers insert upon an aponeurosis 

 which occurs deep between it and the other division, while 

 the main insertion is onto the greater tuberosity of the 

 humerus. The other, more cranial portion, arises from the 

 supraspinous fossa of the scapula and is also inserted onto 

 the greater tuberosity. 



M. infraspinatus (figs. 6, 13, 28) has origin from the 

 whole of the infraspinal surface of the scapula. About 

 midway of the muscle an aponeurosis appears, and from 

 this point it is bipennated. Insertion is by muscle fibers 

 and by a tendon developed from its aponeurosis upon the 

 greater tuberosity of the humerus. 



M. clavo-acromiodeltoideus (figs. 6, 7, 13, 28, 29). 

 In the present genus the clavo- and acromiodeltoids are 

 considered as indivisible, the portions of the muscle cor- 

 responding to these two parts having their fibers converging 

 to a tendinous division between them, so that the appear- 

 ance is that of a single, bipennated muscle. The part 

 corresponding to the clavodeltoid arises from the ventral 

 border of the clavicle, with insertion upon the tendinous 

 division between this and the acromiodeltoid, and upon 

 the medial border of the deltoid ridge of the humerus. The 

 part corresponding to the acromiodeltoid has origin from 

 the cranio-ventral border of the acromion, while insertion 

 is onto the tendinous division common to this and the 

 preceding portion, and upon the lateral border of the del- 

 toid ridge of the humerus. This part of the muscle directly 

 overhes the insertional end of the spinodeltoid. 



In Teonoma the origin of the acromiodeltoid is slightly 

 more extensive. 



M. spinodeltoideus (figs. 6, 28) arises from the caudal 

 border of the entire spine of the scapula, although the 

 dorsal 8 mm. is lightly aponeurotic and without muscle 

 fibers. It passes beneath the acromiodeltoid and is in- 

 serted upon the deltoid ridge of the humerus. 



