THE POSITION OF THE FETUS IN THE UTERUS. 



The position of the fetus or fetuses in the- uterine cavity is 

 largely determined by the form and direction of the cavity itself 

 and the form and specific gravity of the fetus. Since these 

 factors are reasonably constant in each species, it follows that 

 the position of the young in the uterine cavity is also quite 

 uniform. 



It is not alwa3's easy to determine precisely the position of the 

 fetus in the uterus, by post-mortem examination, because of the 

 fact that the fetus and uterus probably change their position 

 somewhat according to that of the maternal body. We have al- 

 ready stated above that the gravid uterus possesses the highest 

 specific gravity of any of the abdominal viscera. The fetus also 

 offers the highest specific gravity among the uterine contents 

 and, this being true, it follows that the position of the fetus 

 should always be stable, independent of its umbilic attachments. 



In the development of the embryo, the head-end grows much 

 more rapidly during the first stages of embryonic life than the 

 posterior portions. The circulation of the fetus is so distributed 

 that more arterial blood reaches the anterior than the posterior 

 end of the embryo, especially during the early stages of fetal life. 

 The brain grows very rapidly and the dorsal surface of the body 

 outgrows the ventral, so that the embryo is soon arciform. The 

 great development of the head-end of the embryo, as compared to 

 the posterior, causes the anterior portion to possess greater weight, 

 which would constantly tend to cause the embryo, if suspended, 

 to rest with its head-end lower than the posterior part of the 

 body. The arciform character of the fetus continues throughout 

 intra-uterine life and, from the beginning, affects the stability of 

 the position of the fetus. 



The fact that the uterine cavity of each of our domestic animals 

 is more or less tubular in form renders it essential that the long axis 

 of the fetus should correspond to the long axis of the uterine 

 cavity, so that regularly the fetus is found resting in this position. 

 Exceptions to this rule occur in the uterus of the mare and, more 



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