Mammalia: Visceral Systems 



661 



V. DORS, peni: 



CORP CAV URE 



A DORS PENIS. 



SEPTUM PENIS" 



A. DORS PENIS 



TUNICA ALBUGINEA 



CORP CAV. PENIS 



;^.> 



FASCIA PENIS 



/ASCIA PENIS 



-CORP CAV. PENIS 



CORP. CAV. URETH. 



Fig. 499. Cross sections of 

 the penis of the rhesus monkey. 



(A) 1 cm. behind the glans. 



(B) 3 cm. behind the glans. 

 (a. dors, penis) Dorsal arteries 

 of penis; (v. dors, penis) dorsal 

 vein of penis. (Courtesy, Hart- 

 man and Straus: "Anatomy of 

 the Rhesus Monkey," Balti- 

 more, Williams & Wilkins Co.) 



present also in the female, but undergo much less differentiation. 

 There is comparatively little elongation of the phallic outgrowth. The 

 urinogenital cloacal space does not become enclosed to form a tubular 

 urethra, but persists as a dorsoventrally elongated but transversely 

 narrow median passage, the vestibule (Figs. 494,495). The internal 

 genital folds, in their more distal region, produce very rudimentary 

 corpora cavernosa which bear distally a rudimentary glans correspond- 

 ing in origin to the glans penis. In the adult these structures constitute 

 the clitoris, which lies in the ventral wall of the vestibule, slightly 

 projecting. Rarely, a small os clitoridis, corresponding to the os 

 penis, is present. The remainder of the internal genital folds become, 

 in the human female, a pair of thin, wide folds, the labia minora, 

 which bound the vestibule laterally (Fig. 495). The external genital 

 folds become a pair of prominent and relatively thick folds, the labia 

 majora, which are laterally adjacent to the labia minora and more 

 or less completely enclose them and the vestibular aperture. In mam- 

 mals other than man, there is usually only a single pair of labia at the 

 vestibular aperture. 



In some cases among insectivores, rodents, and lemurs, the urethral 

 groove in the region of the clitoris becomes enclosed to form a narrow 

 canal separated from the main urinogenital space. This canal becomes 

 joined to the neck of the bladder. Thus an independent urinary outlet 

 for the bladder is provided via the clitoris, leaving the major cloacal 

 space as a genital passage only. 



The approximate correspondence of parts of the human male and 

 female external genitalia, based on embryonic origin, is summarized 

 in the following table. 



