\; 



22 Diseases of the Ge^iital Organs 



In the cow and in most other animals it is identical in form, 

 consistence, and volume with the corpus luteum of preg- 

 nancy, but its color differs. In the n on-p regnant cow it is 

 chocolate-colored. Prior to the next estrum it atrophies. 



Should the ovum become fecundated and undergo normal 

 development, the corpus luteum forming in the crater is al- 

 most always markedly yellow, lemon, or orange. It pro- 

 jects beyond the ovarian surface. It persists regularly up 

 to the time of parturition or abortion and for a varying 

 length of time thereafter. It is known as a true corpus 

 luteum. Pathologically, it sometimes atrophies during 

 pregnancy and is one of the causes of estrum in pregnant 

 animals. While in unipara the corpus luteum regularly 

 atrophies soon after the termination of pregnancy, the 

 atrophy is ordinarily dependent upon the expulsion of the 

 uterine contents. If the fetus perishes, but is retained and 

 desiccates or macerates, the corpus luteum remains. In 

 the sow (and presumably in other multipara) the number 

 of corpora lutea almost always exceeds the number of 

 fetuses, both living and dead, registering the fact that not 

 all ova discharged at a given estrum successfully mature. 

 When very few pigs are born in a litter, it indicates that 

 numerous ova or embryos have perished, rather than that 

 few ova were discharged. The size and form of the ovary 

 are accordingly modified by the presence of a ripe ovisac 

 or ovisacs or of a corpus luteum. In the cow the corpus 

 luteum is frequently larger than the remainder of the 

 ovary — approximately % to % inch. 



2. The Muellerian Ducts 



The beginning of the genital canal in the embryo con- 

 sists of two parallel rods, which later become excavated to 

 form tubes — the ducts of Mueller — extending from near 

 the posterior body opening, upward and forward to the re- 

 gion of the ovary. Eventually the two ducts fuse at their 

 posterior ends, producing a single tube. The ducts become 

 differentiated, through specialization in their development, 

 into four essentially separate segments, each having its 

 distinctive function. The anterior segment constitutes the 



