GENERATIVE ORGANS OF VERTEBRATA. 



G23 



Fig. 356. Divided 

 penis of Didelpkys 

 philander. a b 



Halves of the glans. 

 s Groove on its inner 

 surface. x Region 

 of the anus which is 

 placed behind the 

 orifice of the prepuco 

 (after Otto). 



which are derived from tlie genital protuberance and surround the 

 urogenital canal ; in some they are divided at their free end 

 (Fig. 356, a b) and form the glans penis. The urogenital canal is 

 continued on to each half in the form of a 

 groove (s), and these grooves may unite together 

 to form a canal. In others (Halmaturus) these 

 erectile bodies are connected with two others, 

 with which they unite to form a cylindrical penis, 

 and bound the urogenital canal. The first- 

 mentioned erectile bodies generally fuse very 

 early in other Mammalia to form a corpus caver- 

 nosum urethras which surrounds the urogenital 

 canal (urethra), and of which the most anterior 

 end, which varies greatly in form, forms the glans 

 penis. The two other erectile bodies (corpora 

 cavernosa penis), which in the Marsupialia are 

 not firmly connected with the pelvis, are con- 

 nected with the ischium; they pass above the 

 corpus cavernosum urethras, but do not extend 

 into the wall of the urogenital canal. In most 

 Mammals the penis thus formed extends for- 

 wards from the symphysis pubis along the median line of the 

 abdomen, and ends at a varying distance from the umbilicus ; 

 in others (Chiroptera, Primates), it is free and hangs down 

 from the symphysis pubis. In either case, the integument covers 

 it and forms a fold in front of, and around the glans — the 

 prepuce. 



In the female, the genital protuberance is never developed to 

 the same extent as in the male; it forms the clitoris, which carries 

 on its lower surface the opening of the urogenital sinus, which is 

 bounded by lateral folds. The clitoris is generally more largely 

 developed in the embryo than in the adult, as it projects from the 

 pubic fissure and is afterwards withdrawn into it. In some Apes, 

 however (Ateles), the clitoris continues to be developed and become 

 an organ of some size. Two erectile bodies (corpora cavernosa 

 urethras) lie in the walls of the urogenital sinus and surround it 

 as far as the clitoris, at the base of which there is another pair of 

 erectile bodies. The end of the clitoris is generally provided with 

 a gland, and is also covered by a prepuce. Sometimes this organ 

 is provided with special muscles, which are mostly differentiated, 

 as are also those of the erectile bodies, from a common occludor 

 of the cloaca, such as is seen in the Marsupialia. Iu addition 

 to these, many Mammals have muscles which raise, or retract the 

 penis. 



Glandular organs open into the urogenital sinus of both 

 sexes. There are others besides the prostatic glands already men- 

 tioned (p. 619) ; there may be one or more, or as many as four 

 pairs (Marsupialia); they lie at the root of the penis (Fig. 353, c). 



