64 U.S. NATIONAL MUSEUM BULLETIN 2 73 



Caudal Group 



M. pubocaudalis (figs. 21, 22) : This part of the pelvic sphincter is 

 represented by a rather weak muscular lamina whose fibers arise from 

 the back of the pubic s3nTiphysis and upper pubic ramus on the 

 iliopectineal line. This origin extends up to about the iliopubic junc- 

 tion. The symphyseal fibers pass backward along the sides of the 

 prostate and rectum with the retractor recti et urethrae intervening. 

 They are joined by the pubic fibers, the most posterior of which have 

 an almost transverse direction. Past the rectum the pubocaudalis is 

 inserted on the second and third hemal arches. 



M. iliocaudalis (figs. 21, 22): It is better developed than the 

 pubocaudalis. Its fleshy fibers arise from the linea arcuata below the 

 attachment of m. psoas minor. They pass caudomedially as a muscular 

 sheet superficial to the pubocaudalis, retractor recti et urethrae and 

 the rectum. Insertion is on the fourth and fifth hemal arches and on 

 one of the tendons which from these bones give rise to m. extensor 

 caudae medialis. 



M. ischiocaudalis (figs. 21, 41): This is a strong and fleshy mass 

 which from its origin, by short tendinous fibers on the region of the 

 ischiadic spine, spreads out toward the proximal part of the tail where 

 it is inserted on the costal processes of caudal vertebrae 1 to 7. The 

 ischiocaudalis is proximally covered by the gluteus maximus with the 

 internal pudendal vessels and the pudendal nerve running between the 

 two muscles along the origin of the first. Its deep surface is in relation 

 with the pubo- and iliocaudalis and closes dorsally the narrow space 

 of the ischiorectal fossa. 



M. flexor caudae lateralis: I regard this long and segmentally 

 arranged muscle as the homologue of m. flexor caudae longus of the 

 rhesus monkey (Howell and Straus, 1933). Its fleshy fibers arise from 

 (1) the last lumbar vertebrae and the disk just craniad to it, (2) 

 the pelvic surface of the sacrum lateral to the sacral foramina and, 

 in the tail, (3) the ventral aspect of the caudal costal processes or, 

 in those more distal vertebrae where they have been lost, on (4) 

 the cranial tubercle resulting from their modification. The insertion 

 is by two groups of long tendons: (1) on the tip of the costal processes 

 beginning at Cd 8 or 9 and continuing on the distal costal tubercle 

 down to the end of the tail, and (2) on the ventroproximal sesamoids 

 or tubercles beginning at Cd 8 or 9. 



M. flexor caudae medialis: This is the homologue of m. flexor 

 caudae brevis as described in the rhesus macaque by Howell and 

 Straus (1933), but I prefer to name it differently because of its 

 presence throughout the tail and sacral regions. It arises by fleshy 

 fibers from (1) the pelvic surface of the sacrum medial to the sacral 



