384 



COMPARATIVE ANATOMY 



FIG. 306. (The special thickening of the corpus spongiosum and the glans penis 

 present in some Mammals is not indicated). 



A, Marsupial (very diagrammatic, for comparison with Fig. 305 C ; the obliterated 

 opening of the urinogenital canal into the cloaca is indicated by dotted lines); 

 B, Rodent (Ccelogenys paca) ; C, Ape (Cercopitheai*) : in most placental Mam- 

 mals the apex of the penis does not hang down ; D, Man ; E, Human foetus. 



Additional letterings : a, anus ; 6, pelvic symphysis ; p, genital prominence, which 

 gives rise to the penis or clitoris ; al, stalk of allantois. 



ventral wall of the cloaca. A channel passes along the side facing 

 the cloaca to the opening of the urinogenital sinus : this condition 

 is usually retained throughout life in the case of the clitoris of the 

 female, while in the male (and occasionally in the female also) the 

 groove becomes closed to form a canal continuous with the 

 urinogenital canal or urethra, which thus becomes considerably 

 lengthened. In addition to the paired erectile corpora cavernosa 

 there is a median corpus spongiosum or corpus cavernosum urethrce 

 in connection with the penis (Fig. 307): corpora cavernosa are also 



A 



Ge- 



FIG. 307. A, SEMIDIAGRAMMATIC FIGURE OF THE HUMAN PENIS. (In transverse 

 section and from the side.) B, CLITORIS OF A MONKEY (Cebus capucinus). 



A, albuginea penis ; A 1 , albuginea urethrse ; Sp, septum between the two corpora 

 cavernosa ; S, sulcus dorsalis penis ; Ccp, corpus cavernosum ; Ccu, corpus 

 spongiosum, which gives rise to the glans penis at Gp, and forms an oval 

 enlargement (bulbus) at B ; rd, rd 1 , crura of the corpora cavernosa ; Cli, 

 clitoris, with its ventral furrow (R), glans (Gc), and prepuce (Pp). 



present in the clitoris, and the corpus spongiosum, which retains 

 its paired character, is represented by the so-called bulbi vestibuli 

 at the vulva or entrance to the vagina. 



In many Mammals a bone (os penis) becomes developed in 

 the septum between the corpora cavernosa (e.g., many Marsupials, 

 Rodents, Bats, Carnivores, Whales, Lemurs, and Apes). In some 

 {e.g., Seal) there is an os clitoridis in the female also. The glans is 

 provided with a special kind of tactile corpuscles, and in the male 

 may bear horny papillae and even calcified plates and spines (e.g., 

 certain Rodents). 



