PHYSIOLOGY. 487 



the allantois appears, and in its prolongation the sexual 

 parts. 



2997. Originally the whole chorion is replete alO 

 around with vessels ; but as the process of oxydation V 

 occurs most powerfully upon the fundus uteri, so are 

 the vessels developed most abundantly in that very situa- 

 tion, and form the placenta. 



2998. The placenta is no peculiar organ, but only the 

 more energetic part of the chorion. 



2999. It must necessarily be placed around the inser- 

 tion of the umbilical cord, because at this spot the inver- 

 sion takes place, on account of the strong oxydation. 



3000. The placenta is always situated upon the fundus 

 uteri, because it originates only through its influence. It 

 cannot therefore begin to suck, like the mouth of a leech, 

 in a fortuitous or voluntary manner anywhere. If it is 

 found occupying some other situation, it is a proof that 

 the oxydizing process of the uterus has been displaced. 

 This is consequently an abnormal situation. 



3001. Opposite to the foetal vascular system is first of 

 all developed the general system of animal life, namely, 

 the nervous system, and indeed the spinal chord, or what 

 has been called the ' carina' or primary streak. 



3002. The development of all other systems oscillates ) 

 in this antagonism of blood and nerves. 



3003. In the antagonism of the placenta is formed the 

 liver, which in the embryo is one of the largest organs, 

 and in its antagonism the brain is developed. 



3004. In the antagonism of the amnion the integu- 

 ment is evolved, and in its antagonism the branchiae 

 and lungs. 



3005. In obedience to the antagonism of the arteries 

 and veins, the vitelline sac divides into small and large 

 intestine. The one pursues a course towards the arterial 

 extremity of the body, the brain, the other towards the 

 venous or sexual parts ; mouth and anus. 



3006. Finally, from the antagonism of the allantois 

 the sexual parts emerge at the very extremity of the 

 body, which is placed opposite to the mouth. 



