V 



INTERNAL ORGANS OF GENERATION. 37 



tissue, which also unites it to the bladder, is here close and firm, and 

 this fact may serve to explain why the rectum is so rarely involved 

 in displacements of the uterus ; while the bladder is always more or less 

 so. Laterally, it is attached to the muscular and aponeurotic structures 

 in the cavity of the pelvis. Internally^ it is lined by a thin mucous 

 membrane, which is always abundantly covered with mucus (in women 

 this mucus is acid, while that of the uterus is alkaline), and is disposed 

 (in the Mare) in longitudinal rugse, which are more conspicuous after 

 several births. These rugae no doubt favor the dilatation of the canal 

 during coitus or the passage of the fcetus ; a transverse ridge, already 

 described as existing on the lower face of the canal, covers the meatus. 

 This membrane is continuous with that of the vulva, and anteriorly, at 

 the cul-de-sac, it is reflected over the cervix of the uterus, which projects, 

 like a cauliflower in shape, into the cavity. It is provided with papillae, 

 and covered with pavement epithelium. It usually has a pale pink hue, 

 but at the period of oestrum its color becomes heightened to a bright 

 red, and its secretion is considerably increased. 



Externally, the vagina is invested by a muscular coat which is en- 

 veloped by an abundant layer of connective tissue, and traversed by a 

 large number of blood-vessels ; in front, however, this tunic is invested in 

 peritoneal membrane, which is folded in a circular manner around it 

 to pass over the uterus. 



The vagina is supplied with blood by the internal pudic artery; its 

 veins are disposed as a plexus around it, and terminate in the satellite 

 trunk of the artery. The vagina serves for copulation and the passage 

 of the foetus. At the periods of oestrum and parturition, the mucous 



''secretion is more active than at other times. In youth it is contracted ; 

 after copulation its dimensions are increased, and these are greatest dur- 

 ing parturition. In old age it is much diminished ; in the third or fourth 

 months of gestation in the larger animals, it becomes elongated from dis- 



gjlacement of the uterus, which is carried farther forward into the abdomi- 

 nal cavity; towards the termination "of this process, its length diminishes 

 as the uterus acquires increased volume, and to such an extent does this 

 occur, that at the commencement of parturition, if the fcetus is large, and 

 especially if there be two foetuses, the posterior wall of that receptacle, 

 pushed back into the pelvis, nearly or entirely effaces the cavity of the 

 vagina, and even in some instances thrusts it between the labia of the 

 vulva or beyond. 



Differences. 

 Cow, Sheep, and Goat. 



In the Cow, the canal is longer and wider than in the Mare ; the mu- 

 cous membrane of the vagina is thicker, is disposed in transverse rugai 

 as in the human species, and at each side of the passage for a certain 

 distance, between the mucous and muscular layers, there exists a mucous 

 canal that opens into the vulvular cavity, in front of, and at the side of 

 the meatus. 



The uses of these canals, which are not present in the Sheep or Goat, 

 and rarely in the Mare, and which are usually known as the " canals of 

 Gaertner," are unknown. They pass backwards into the broad ligaments 

 of the uterus, and terminate in a cul-de-sac. They have some function 

 during foetal life. 



