40 ANATOMY OF THE WOOD RAT 



sternoscapularis present. It is a short, slender muscle 

 which is easily overlooked, arising from the cartilage of 

 the first rib, and is inserted upon the distal end of the 

 clavicle. 



M. serratus magnus (figs. 6, 7, 9, 29). The fibers upon 

 the cranial border of this muscle are separable from the 

 levator scapulae only with difficulty, but as the origin is 

 distinct, the insertion fairly so, and the innervation of the 

 two is not the same, there is no reason why they should not 

 be considered as constituting separate muscles. Origin is 

 by fleshy digitations from the cranial border of five ribs — 

 the fifth to ninth inclusive. Insertion is by muscle and 

 tendon fibers upon the caudal portion of the vertebral 

 border of the scapula, and this is twisted upon itself in 

 characteristic fashion. 



In Teonoma this muscle is similar except that origin is 

 from six ribs — the sixth to eleventh inclusive. 



M. levator scapulae (figs. 9, 29). This hardly seems 

 the proper place for this muscle, and an attempt was first 

 made to treat it as a division of the serratus, but such is 

 not possible, for its innervation is different from that of the 

 serratus, and it was found to be a speciahzed levator 

 scapulae, as termed in most works on the lower mammals. 

 A better name for it would really be depressor scapulae, 

 as that is its present function brought about by the change 

 in the relational position of the shoulder due to the posture 

 of the animal; but it was thought wiser to retain the usual 

 term. It has origin from the transverse processes of the 

 last five cervical vertebrae and the first four ribs. The 

 original portion of the muscle is about 25 mm. in width. 

 Most of it emerges dorsad from beneath the dorsal border 

 of the scalenus; but the portion arising from the fourth 

 rib constitutes, in reality, a separate head, for it progresses 

 dorsad from its origin for several millimeters between the 

 bellies of the two longer divisions of the scalenus before 



