OSTEOLOGY 145 



appreciable variation is the teres minor, slightly larger in 

 Neotoma and Teonoma. The shape of the greater tuberosity 

 is uniformly the same, being a trifle irregular and with a 

 slight depression upon the lateral portion. The tuberosity is, 

 however, somewhat smaller in Neotoma, and larger in 

 Teonoma, and in some specimens of both of these it extends 

 above the head, which it never does in Homodontomys. 



The lesser tuberosity is but a third the size of the greater 

 and hes mediad to the head. The subscapularis is the only 

 muscle attached to it, and it varies more in size individually 

 than it does subgenerically ; but is lighter in Neotoma. Be- 

 tween the lesser and greater tuberosities lies the bicipital 

 groove, over which passes the original portion of the biceps 

 brachii. 



Extending distad from the lesser tuberosity is the medial 

 ridge, culminating at the first third of the humeral length 

 in a faint process, distad from which extends the usual 

 medial border of the shaft. Extending caudad from the 

 medial ridge, between the tuberosity and the process, is the 

 insertion of the pectoralis abdominaUs. In Teonoma this 

 ridge is best developed, but this may be due more to me- 

 chanical than myological reasons. Upon the medial process 

 of the shaft, above described, are inserted the teres major 

 and latissimus dorsi, but the latter seems to occupy the most 

 prominent portion of the process, and the development of the 

 latter doubtless depends mostly upon this muscle. Its most 

 prominent development is certainly found in Teonoma, but 

 there is much individual variation in this respect and one 

 hesitates to make definite statements concerning it. 



Extending distad from the greater tuberosity upon the 

 cranio-lateral border of the humerus is the deltoid ridge, 

 culminating in the spine of the same name. It is highly 

 developed in the present genus and the factors influencing 

 its size are complex. Along the medial border of the proximal 

 portion of the deltoid ridge are inserted the panniculus 



