32 Veterinary Obstetrics 



The peritoneal covering extends backwards from the anterior 

 extremity three to five inches in the mare, where it becomes re- 

 flected upon the rectum, bladder and pelvic walls. In the poste- 

 rior portion of its course the vagina is surrounded by the loose 

 pelvic connective tissue, which permits comparatively free move- 

 ment. 



The function of the vagina is chiefly copulative, receiving the 

 penis of the male during coition ; and during parturition it 

 affords a passage for the fetus from the uterus to the vulva. 



In the mare, the organ has the power of ' ' ballooning ' ' or in- 

 flating under sexual excitement or physical excitation. In this 

 state it expands to such a degree that it fills the pelvic cavity 

 completely from side to side and from floor to roof, presenting a 

 vast cavity with smooth, rigid walls, which laterally are in close 

 contact with the bony or ligamentous pelvic walls, while, superi- 

 orly they lie against the sacrum except in the area where the 

 rectum intervenes and inferiorly with the pubis except for the 

 urinary bladder. 



The physiological nature of this "ballooning" has not been, 

 determined ; apparently it is of an erectile character. It prob- 

 ably increases the safety of copulation by rendering it impossible 

 for folds of the vagina to become caught by the penis and 

 injured. This power of ballooning differs largely from other 

 hollow organs of the body. 



The vagina of the cow has a similar ballooning power but of a 

 less degree and it is possibly a general function, though less 

 marked, in the vaginae of other animals. 



The ballooning of the vagina of the mare is easily induced by 

 intravaginal manipulation, by the injection into the organ of 

 bland, tepid fluids or by various other means. The phenomenon 

 is especially marked and easily induced by introducing the moist 

 hand into the organ at the time of estrum when the inflation at 

 once occurs. 



The hymen is a transverse membranous expanse stretching 

 across the genital canal marking the boundary between the: 

 vagina and vulva. It represents the partition between the term- 

 ination of the hind gut and the proctodeum of the embryo, which 

 has failed to disappear in the lower or geni to- urinary division of 

 the cloaca. Generally it atrophies and completely disappears in 

 our domesticated animals before their birth but at times it per- 



