Pregnancy, or Gestation. 371 



the uterine cotyledons develop rapidly and it has been shown 

 that new ones appear. Rainard could distinguish but 30 to 40 

 cotyledons in the uteri of heifers or lambs, while, after parturi- 

 tion, he found 100 or more. It has further been shown by the 

 experiments of Colin and others that, if the cotyledons have been 

 artificially removed from a cow, new ones form during the period 

 of pregnancy. In the mucous membrane of the uterus, there also 

 form crypts, at an early period in pregnancy, into which the villi 

 of the fetal chorion grow and become attached. These crypts 

 are the counterpart of the villi of the chorion and vary in their 

 form and complexity according to the species of the animal. 

 They are lined with a thin layer of epithelium, immediately be- 

 neath which are the uterine capillaries, in a rich net-work. In 

 the mare these crypts are distributed over the entire uterine sur- 

 face, in harmony with the distribution of the villi of the chorion, 

 while in the cow they are limited to the cotyledons and consti- 

 tute essentially the mass of these organs during pregnancy. In 

 those animals having zonular placentae-, they are confined to 

 the placental zone. 



Between the mouths of these crypts, utricular glands open 

 upon the surface of the mucous membrane and pour out their 

 secretions, the uterine milk. (See Fig. 78.) 



Investigations have shown that during pregnancy the muscle 

 fibers of the uterus become increased in size and multiplied in 

 numbers, so that the increased volume of the organ is not wholly 

 dependent upon increased function in some of the muscle cells, 

 but partly upon a multiplication of the muscle fibers. The 

 lymphatics and nerves also increase in extent and volume during 

 pregnancy. 



The broad ligaments of the uterus become increased in 

 their length and thickness and their muscle fibers in volume. 

 Fleming asserts that the muscle fibers are increased in order 

 to give them sufficient strength to sustain the weight of the 

 greatly enlarged uterus and its contents. This cannot be cor- 

 rect, because the gravid uterus lies upon the floor of the abdomen 

 and does not swing in the ligaments. The increase in the extent 

 and strength of the broad ligaments should be attributed rather to 

 the necessity for their maintaining their relations with the uterus 

 in its changed position and for preventing their rupture during 



