30 OBSTETRICAL ANATOMY. 



excitation during coition. It is present in all the domestic female 

 animals, and is frequently erected while they are in " heat," as well as 

 in the act of copulation. It is abundantly supplied with nerves, which 

 endow it with most acute sensibility, and the mucous membrane 

 enveloping it is usually dark coloured or marbled, though in white 

 Mares it may be colourless. 



The meatus urinarius is the orifice of the urethra, which is a very 

 short canal in the female. This canal passes immediately beneath the 

 anterior sphincter muscle of the vulva, and after a brief course (about 

 two inches) in the textures composing the floor of the vagina, opens 

 into the vulvar cavity at from four to six inches from its exterior. This 

 opening, which is on the floor of the cavity, is covered by a wide dupli- 

 cature of the lining membrane that acts as, and is designated, the valve 

 of the meatus or vagina (valvula vagince) ; its free border is turned 

 backwards, and it would thus appear to direct the urine towards the 

 external opening of the vulva, and prevent its reflux into the vagina. 

 Eainard states that this valve is more extensive as the vagina is narrow, 

 and consequently as the female is young ; it has been compared to the 

 hymen of woman. Brugnone was of opinion that it was attached to 

 the upper surface of the vagina by a small cord, and that it was the 

 rupture of this by the forced entrance of the penis which caused the 

 slight flow of blood from the vulva observed in Mares put to the horse 

 for the first time. This is no doubt the hymen to which he refers — a 

 membrane found generally in the i'illy, though not often in the Mare, 

 but which, when present, separates the vulvar from the vaginal cavity. 

 This membrane forms a circular partition, fixed by its circumference to 

 the vulvo- vaginal walls along with the valve of the meatus, and is 

 perforated by one or more openings, which are sometimes very small. 



The existence of the hymen in animals has been denied, but that it is 

 present sometimes, though rarely, there can be no doubt, and, as in 

 woman, when imperforate it leads to retention of secretions. Not 

 infrequently old brood Mares show in this situation pediculated appen- 

 dices, which are the debris of this mucous septum. 



The urethral orifice of the Mare is wider than that of the Horse, and 

 will readily admit a large catheter. In passing that instrument, it is 

 well to remember that the urethral canal curves forward and downward, 

 and that the valve must be raised either with the point of the instru- 

 ment or the finger before the passage can be entered. 



In ordinary circumstances the vulva is retracted, and with Mares 

 which have foaled several times the labia usually exhibit as many 

 wrinkles or folds as parturition has been frequent. 



During oestrum, but especially towards the termination of pregnancy, 

 the labia become tumified and soft, the inferior commissure descends, 

 the vulvar opening is enlarged, and from it is discharged a quantity of 

 tenacious stringy mucus. 



Differences in the Vulva of other Animals. 



Cow. 



In the Cow the lips of the vulva are larger, softer, and thicker than 

 in the Mare, and the inferior commissure, angular and prolonged into a 

 curved peak, is furnished with a tuft of hair. The meatus urinarius is dis- 

 posed as in the Mare ; but in the interior of the urethral canal, fixed to its 



