52 ANATOMY OF THE WOOD RAT 



The transverso-spino-occipital system of the deep back 

 musculature is composed of three muscles — the 



Mm. biventer cervicis multifidis spinae 



complexus 



The first two of these in the present animal constitute 

 separate divisions of what is often termed the semispinahs 

 capitis. 



M. biventer cervicis (figs. 10, 11, 24). Like so many 

 other muscles of the vertebral column, this one shows con- 

 siderable individual variation in its attachments, which 

 fact, however, is probably of no practical significance to 

 us. In addition, it is well to mention that this is one of the 

 muscles concerning whose exact limits of extent it is ex- 

 tremely difficult to feel certain. 



The caudal portion arises by two heads. The more 

 posterior has origin from the third and fourth to sixth 

 or seventh (inclusive) thoracic vertebrae, while the anterior 

 slip arises from the vertebrae extending from the third 

 thoracic to the axis. Passing craniad, the anterior slip 

 develops an aponeurosis upon its ectal belly and upon the 

 superficial surface of this the posterior slip is inserted. 

 The aponeurosis is, in turn, inserted upon the superior 

 angle of the occiput from its center to the slight tuberosity 

 at its ventro-lateral termination. 



In Teonoma the posterior slip arises from the fourth or 

 fifth to seventh or eighth thoracic vertebrae, and the 

 anterior one, from the fifth thoracic to the fourth (or some- 

 times third) cervical vertebra. It is shghtly more robust 

 in this subgenus, and the junction of the two slips occurs 

 at a point somewhat more caudad. 



M. complexus (figs. 8, 10, 11, 23, 24). Origin of this 

 muscle, between the longissimus cervicis and biventer 

 cervicis, is from the last three cervical and possibly the 

 first thoracic vertebrae. It converges craniad and the 



