50 ANATOMY OF THE WOOD RAT 



and ventro-laterad to the mastoid process of the squamosal. 

 Careful examination discloses the fact that in reality the 

 lateral 3 or 4 mm. constitutes a separate slip, the origin 

 of which is hardly to be separated from the main belly, 

 but with a distinct insertion, by aponeurosis, beneath the 

 lateral portion of the larger mass. It should be noted that 

 this is the deepest muscle arising from the nuchal hgament. 



In Neotoma the whole muscle is slightly more robust. 

 In Teonoma the origin extends closer to the occiput, and 

 the lateral slip is even better differentiated. 



This muscle is served by branches of the cervical and 

 probably the thoracic nerves as well. 



The long system, or sacrospinal musculature of the 

 back, is most conveniently divided into the 



Mm. iliocostales spinalis dorsi 



longissimus dorsi 



M. iliocostales (figs. 10, 11) he upon the dorsal side of 

 the ribs laterad to the longissimus dorsi. The bundles 

 extend craniad from the eleventh rib, with origin in groups 

 of fibers and small tendons from this to the third (inclusive) 

 rib. Each group is inserted (apparently) upon the fourth 

 rib craniad of its origin, but there is no attachment to the 

 second rib. The muscle as a whole is inserted by tendon 

 fibers upon the first rib and the transverse processes of the 

 sixth and seventh cervical vertebrae. 



In Teonoma origin begins at the tenth rib, and the muscle 

 is free from the third rib as well as the second. 



M. longissimus dorsi (figs. 6, 9, 10, 11, 12, 32, 33). 

 The several subdivisions of this muscle are not very well 

 differentiated in the present animal. Pars cervicis, 

 often obscure but here separable into a distinct muscle, is 

 figured as the longissimus cervicis. It is situated be- 

 tween the thoracico-lumbar portion of the same muscle 

 and biventer cervicis, with origin from the transverse 



