20 



LIVE-STOCK JUDGING 



occurrence, except in rare instances, prohibits the sub- 

 sequent appearance of oestrum. 



25. Gestation. — The duration of gestation is usually 

 correlated with the size and longevity of the species, being 

 three weeks in the case of the mouse and twenty-two 



Fig. 9. — Generative organs of the mare, a, right ovary ; 6, right ovi- 

 duct ; c, right uterine horn ; d, left uterine horn ; e, body of the 

 uterus ; ei, vaginal part of uterus ; 62, mouth of uterus ; /, broad liga^ 

 ment ; /i, suspensory ligament of the ovary ; fi, round ligament ; 

 0, vagina; h, vulva; i, vulvar cavity; ii, poster! or commissure; 

 12, anterior commissure ; k, muscle constrictor cunni ; m, corpus 

 cavernosum vestibule ; n, abdominal wall ; u, left kidney ; p, left 

 ureter ; r, bladder ; s, urethra ; (, rectum ; u, anus ; v, external sphinc- 

 ter muscle of anus ; w, point where the levator ani muscle passes 

 under the external sphincter ; x, levator ani muscle ; y, longitudinal 

 fibers of the rectum ; yi, posterior band of fibers ; z, muscle constric- 

 tor vestibule; 1, utero-ovarian artery; li, branch to the ovary; 

 I2, branch to the horn of the uterus ; 2, external uterine artery ; 

 3, umbilical artery ; 4 and 5, sections through pelvic bone. 



months in the case of the elephant. There is established 

 following conception, and through the medium of a special 

 development of the walls of the pregnant uterus and of 

 the membranes enveloping the embryo, a temporary cir- 

 culatory system, by means of which the blood of the dam 



Digitized by Microsoft® 



