380 Veterhiary Obstetrics 



rarely, in other animals in which a single fetus develops more or 

 less equally in each of the two coruua, but even in this instance 

 the rule is followed in a measure by the fetus being placed 

 longitudinally in the combined cavities of the two cornua. This 

 compels the fetus to assume a transverse position in relation to 

 the long axis of the body of the mother and of the body of the 

 uterus. The question of the development of the fetus in the 

 two horns is discussed under " Bi-cornual Pregnancy." 



The question of the presentation of the anterior or posterior 

 end of the fetus toward the os uteri is largely determined, so 

 far as we know, by the inclination of the uterus and comparative 

 specific gravity of the head and tail ends of the fetus. Early in 

 embryonic life, as we have already related, the fetus floats free 

 in the amniotic sac and may turn upon its short axis, so that 

 either the head or tail may present toward the os uteri. In the 

 mare and carnivora there is further facility afforded for the fetus 

 to turn upon its short axis, by the complete allantoic .sac. This 

 entirely surrounds the amniotic sac, so that the fetus with its 

 amnion may turn within the allantois. Turning upon the 

 short axis must necessarily cease as soon as the long axis of the 

 fetus exceeds the transverse axis of the uterine cavity. The 

 fetus then becomes fixed, so far as its antero-posterior diameter 

 is concerned, for the remainder of its intra-uterine life. 



In the uniparous and biparous animals, the bases of the 

 uterine cornua slope more or less backward and downward from 

 their anterior attachments toward the os uteri and maintain 

 this position until the weight of the fetus and its membranes, 

 with that of the contained fluids, bears the organ down to the 

 abdominal floor. During this period, prior to the descent of the 

 uterus upon the abdominal floor, the head-end of the fetus is 

 much the heavier and consequently tends to become directed 

 toward the os uteri. A further influence in reference to the 

 position of the fetus is the question of the form of the uterine 

 tube itself. This tube is not uniform in its transverse diameter, 

 but is tapering and becomes smaller as the oviducts are approached, 

 so that again the tendency would be for the larger end of 

 fetus to occup3^ the larger end of the cornu, which would cause 

 the head-end to present toward the os uteri. 



In multiparous animals, in which the uterus lies upon the 



