MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 63 



M. sphincter urethrae: It is like that of the male, but I did not see 

 an m. retractor cloacae. Both m. caudoanalis and m. caudorectalis 

 are more feeble than in the male specimens. 



Sirena (1871) found also the bulbocavernosus of the male to be 

 smaller than m. ischiocavernosus. He describes a m. transversus 

 perinei but the arrangement of fibers in the urogenital diaphragm 

 does not justify, in my opinion, the separate description of a trans- 

 versus. The retractor recti et urethrae he calls m. levator ani. In other 

 respects the perineal musculature of the animals studied by Sirena 

 (1871) corresponds with that of the red howler. He did not find a m. 

 ischiourethralis, however, and was not able to study the region in a 

 female. 



Nerve supply: Mm. bulbospongiosus, ischiocavernosus, and ischio- 

 urethralis receive separate twigs from the perineal branch of the 

 pudendal nerve. The sphincter uretlu-ae is innervated by the dorsal 

 nerve of the penis. Several rami from the inferior hypogastric plexus 

 enter the retractor recti et urethrae. I could not determine the nerve 

 supply of either the caudoanalis or caudorectalis. M. sphincter ani 

 externus has the usual innervation by the inferior rectal nerves. The 

 nerve supply in the female is equivalent. 



Comparative anatomy of the perineal group. — The perineal 

 musculature was the object of two extensive studies by von Eggeling 

 (1896) and Elftman (1932). The former observed several cebids: 

 1 female Ateles ater {=A. paniscus), 1 female Ateles sp., 1 male Ateles 

 ater (= Ateles paniscus), 2 Ateles geqffroyi (= Ateles geqffroy), 1 male 

 Cehus hypoleucus {—Cehus capucinus), 1 male Cebu-s fatuellus {=Cebus 

 apella). Elftman (1932) studied only Cehus among the platyrrhines. 

 Forster (1926) was concerned solely with the means of fixation of the 

 sphincter ani externus as an indication of adaptation to the mobility 

 of the prehensile tail. Hill (1962) describes briefly the bulbo- and 

 ischiocavernosus muscles in the woolly spider monkey. Nothing seems 

 to have been done about Lagothrix. The arrangement of the perineal 

 musculature in Ateles, Cehus, and Brachyteles appears to be the same 

 (see von Eggeling, 1896; Elftman, 1932; Hill, 1962) as in Alouatta. 

 The spider and the howling monkey share the separation of the anal 

 sphincter from the tail by a large space filled with an areolar fatty 

 mass and this muscle is, on the other hand, intimately connected to 

 the urogenital sphincter. Forster (1926) spoke of this condition as an 

 adaptation to the prehensibility of the tail. The poor differentiation 

 of the sphincter lo-ethrae which is formed by a mixture of aponeurotic 

 and muscular fibers, the lack of a fascia diaphragmatica urogenitalis 

 inferior and the absence of an m. levator penis are characters common 

 to all these cebids. 



