116 DISSECTION OF THE DOG 



to just beyond the margin of the ischium, where it is continuous with the 

 uro-genital sinus. 



The interior should be exposed by making a longitudinal incision in the 

 mid-ventral line. When this has been done, there will be no difficulty in 

 determining the extent of the vagina, for its conspicuous longitudinal folds 

 of mucous membrane cease abruptly at the junction of the vagina and the 

 uro-genital sinus. 



The projection of the vaginal 'portion (portio vaginalis) of the cervix of 

 the uterus into the vaginal cavity should be noticed. 



Sinus tjro-genitalis. — The uro-genital sinus is a short tube with a com- 

 paratively smooth interior. Just about the point of junction of the vagina 

 and uro-genital sinus, the ventral wall of the latter is pierced by the external 

 opening of the urethra (orificiurn urethrse externum). 



Partes genitales externa. — The external opening of the genital canal 

 or vulva is in the form of a vertical slit with a rounded dorsal and a sharp 

 ventral commissure. The margins of the opening are formed by prominent, 

 rounded labia pudendi. 



Immediately within the ventral commissure is the clitoris, the homologue 

 of the male penis. 



Muscles of the external genital parts. — The sphincter ani muscle is divisible 

 into two parts, both more or less continuous with muscular fibres of the perineum. 



The oral part of the sphincter is continued almost completely towards 

 the vulva as an ano-vulvar muscle. The aboral portion of the sphincter is 

 only partially continuous with a perineal muscle also running to the vulva. 



The vulva is provided with a constrictor muscle connected with the two 

 perineal slips just mentioned and consisting of external (aboral) and internal 

 (oral) parts. 



A. hypogastrica. — The hypogastric artery has the same origin and the 

 same general disposition as has the corresponding vessel of the male. Naturally, 

 however, there are certain differences dependent upon the differences in the 

 organs of the two sexes. 



From the ramus visceralis (internal pudendal artery) springs a large branch 

 from which the uterine and the cranial and caudal vesical arteries arise. The 

 uterine artery (a. uterina) follows the body and cornua of the uterus. The 

 cranial vesical artery (a. vesicalis cranialis) supplies the bladder mainly, but 

 in addition sends twigs to the vagina. The caudal vesical artery (a. vesicalis 

 caudalis) is mainly concerned in the nourishment of the vagina and the 

 uro-genital sinus. 



The terminal branches of the internal pudendal artery are concerned hi 

 the supply of blood to the uro-genital sinus and the vulva. 



The ramus parietalis of the hypogastric artery comports itself as in the male. 



The rest of the dissection of the female pelvis proceeds on the fines given 

 for the male. 



