44 ANATOMY OF THE WOOD RAT 



the inferior tuberosity of the ischium just caudad of the 

 symphysis to the anterior crest of the iUum, and to it are 

 attached the three muscles of the abdominal wall. 



In Neotoma and Teonoma origin is from the last ten ribs, 

 beginning at the fourth instead of the fifth. 



M. obliquus abdominis internus (fig. 10) has origin 

 from the ental surface of the lumbodorsal fascia, but the 

 anterior portion is not clearly separable from the serratus 

 posterior inferior. Origin is also from Poupart's ligament. 

 Insertion is onto the caudal border of the posterior costal 



,sp'vnil.-\aift5. dorsl 



icrrit. ■post. Inter 



iS^pwiaA-iorsi/ 



V 'hwcN cent — ^ 



I 'Yotig. cerv. 

 ; . '\oTv^. dorsl 



■vL/'-'Lliocost. 



Fig. 10. Deeper muscles of the trunk and neck of Homodontomys 



cartilages and onto the fascia covering the transversalis 

 some distance dorso-laterad of the rectus abdominis. 

 The ventral portion of the muscle is separable from the 

 transversalis only with so much difficulty that the fibers 

 of the internal oblique present the appearance of being in- 

 serted directly upon the deeper muscle. 



M. transversalis (figs. 7, 10) has origin from the medial 

 border of those costal cartilages caudad to the diaphragm, 

 and from some of the fibers of the latter, as well as from 

 the fascia deep to the internal oblique. Insertion is upon 

 the aponeurotic sheet investing the ental surface of the 

 rectus abdominis and upon Poupart's ligament. 



M. cremaster is present only in the male, and its situa- 



