MAY, 1921. AMERICAN MARSUPIAL, CENOLESTES OSGOOD. 39 



Extensor caudae lateralis. Origin by slips from the articular processes 

 of the sacral and caudal vertebrae. Insertion on the sides and transverse 

 processes of the caudal vertebrae. Lies between the abductor caudae 

 externus and the multifidae which are continued to the base of the tail 

 as an extensor caudae medialis. 



Pubococcygeus. Origin from the whole inner caudal border of the 

 pubic ramus. It forms a thin sheet over the obturator foramen and 

 continues fleshy to the front of the fifth caudal vertebra whence it finds 

 attachment in the aponeurosis on the surface of the tail. In some cases 

 it is slightly tendinous on its inner side and attached to the chevron bone 

 of the fifth caudal. Laterally it has slight attachment to the colon. 



Sacrococcygeus. Origin from the ventral surfaces of the transverse 

 processes of the sacral and the first four caudal vertebrae. Thence by 

 numerous slender tendons it proceeds along the side of the tail to the 

 distal caudal vertebrae. These tendons lie slightly laterad of those of 

 the infracoccygeus and fill the space between the cephalic articular and 

 transverse processes of the caudal vertebrae. Its muscular heads are 

 thick and fleshy and lie between the caudal part of the infracoccygeus 

 and the pubococcygeus and ventrad of the ischiococcygeus. 



Ischiococcygeus. Origin from the inner side of the ilium from a 

 point opposite and slightly craniad of the caudal border of the gluteus 

 minimus caudad about halfway to the tuberosity of the ischium. In- 

 sertion on the tips of the transverse processes of the first four caudal 

 vertebrae. 



Iliococcygeus. Origin from the ischial border of the ilium from a 

 point just caudad of the sacrum (posterior inferior spine of ilium) and 

 thence caudad along the whole inner surface of the ilium (great sacro- 

 sciatic notch) nearly to the anterior border of the obturator foramen. A 

 few fibers rise from the tendons of the psoas minor and at this point are 

 closely connected with those of the pubococcygeus. Insertion by four 

 distinct tendons which converge to the middle of the ventral surface of 

 the tail. The outer tendon runs just laterad of the mid-ventral line of 

 the tail to the chevron bone of the eighth caudal vertebra. The next 

 one runs similarly to the seventh caudal. The inner pair of tendons run 

 first mediad, then entad, and finally laterad of the outer pair. Of this 

 inner pair the outer one inserts on the chevron bone of the ninth and the 

 other on the tenth caudal. Near their attachments each of the tendons 

 gives off a slight muscular fasciculus. 



Infracoccygeus. Origin from the medio-ventral surfaces of the 

 bodies of the fifth and sixth lumbars and the two sacral vertebrae. In- 

 sertion by long slender tendons running on the ventral side of the tail 

 next to the median line. The innermost tendon runs to the middle of 



