48 ANATOMY OF THE WOOD RAT 



hardly separable from, the origin of the rhomboideus pos- 

 ticus. The insertion, however, is quite distinct, and the 

 part at right angles to the scapular border is stronger and 

 more extensive. 



M. rhomboideus posticus (figs. 6, 28, 29) has origin 

 chiefly from the greatly developed spine of the second tho- 

 racic vertebra. Insertion is for about 8 mm. along the 

 dorsal border of the scapula, from the insertion of the 

 levator scapulae to 3 mm. craniad of the scapular spine. 

 The ental fibers of this muscle are not so readily separable 

 from the rhomboideus anticus. 



M. occipitoscapularis (rhomboideus capitis or levator 

 scapulae dorsahs) (figs. 6, 8, 24, 28) has origin for a distance 

 of 10 mm. along the lambdoidal portion of the cranium 

 dorso-mediad from the mastoid process of the squamosal. 

 Insertion is upon both the dorsal border of the scapula 

 cranially adjacent to that of the rhomboideus anticus, and 

 upon the extreme dorsal portion of the scapular spine. 



These three foregoing muscles are served by nerve 

 branches from the brachial plexus. 



M. atlantoscapularis (figs. 6, 7, 8, 28). This muscle 

 is usually termed the levator claviculae or levator scapulae 

 ventralis, but atlantoscapularis is preferable. It is a rather 

 slender muscle having origin from the ventral arch of the 

 atlas, with an insertion that is chiefly aponeurotic upon the 

 border of the metacromion. 



The innervation of this muscle is by a branch of the 

 third cervical nerve. 



Third layer of the superficial, secondary back muscles is 

 made up of the 



Mm. serratus posterior superior 

 serratus posterior inferior 



M. serratus posterior superior (figs. 6, 10). There 

 is some individual variation in the origin of this muscle. 



