TYPES OF (ESTROUS CYCLE 



47 



the uterus is constricted and anaemic. At prooestrus dilation 

 of the lumen has begun and at the time of ovulation the uterus 

 has increased to about twice the normal diameter; the stroma 

 and muscular material are then very much attenuated. The 

 increase in size is caused solely by the distension of the lumen. 







i?^'*^ 



Fig. 21. — Uterus of Mouse during Dicestrus. 



During metoestrus the uterus gradually returns to its dioestrous 

 size, and in the unmated animal no further change takes place 

 until the next prooestrus. During pseudo-pregnancy, however, 

 growth of the stroma takes place, and at the end of pseudo- 

 pregnancy, correlated with the atrophy of the corpora lutea, a 

 certain amount of haemorrhage into the lumen may occur. 



Vaginal cycle. The vaginal changes during the oestrous cycle 

 are also very pronounced and are now used for the detection of 

 the oestrous cycle in the intact animal. During prooestrus the 



