CHORION. 161 



■whether physical or physiological. Does it contain nerves and 

 lymphatic, sanguineous, exhalent and inhalent vessels? 



These two last mentioned kinds of vessels having only been ad- 

 mitted in animal bodies upon the say so of the physiologists, espe- 

 cially Bichat, who never saw them, it is good philosophy to reject 

 their existence without discussion, until they shall have been demon- 

 strated by more conclusive proofs. The same may be said of the 

 lymphatics, which the imagination alone of Schroeger and some 

 others seems to me to have detected in the chorion. As to nerves, I 

 think I may say without offence to Chaussier, MM. Ribes, Home, 

 and Bauer, that they are no more to be found there, than the ex- 

 halents and lymphatics. 



421. The question in relation to blood-vessels deserves much 

 more attention. Admitted by a great many savans of the highest 

 merit, and that too upon a certain num.ber of proofs; rejected by 

 other authors not less able, and upon considerations not less powerful, 

 it becomes, upon that account merely, very difficult to settle one's 

 opinion in relation to them. 



In attempting to separate the reflected anhistous coat from the 

 exterior surface of the chorion, we soon perceive an indefinite num- 

 ber of filaments passing from each one of these laminae to the other, 

 and which are more numerous as we approach the circumference of 

 the placenta, or are nearer to the commencement of the pregnancy. 

 ' But these filaments which Sandifort and others mistook for vessels, 

 are nothing but the remains of the villous tomentwa of the ovule, 

 and not canals carrying on any circulation whatever. The chorion 

 exists before the embryo; with the exception of the portion that is 

 to support the placenta, it is completely separated from the womb 

 by an inert stratum; the umbilical and placental vessels do not make 

 their appearance in the new being until the ovule attaches itself to 

 the internal surface of the uterus; it is only, therefore, in the area 

 circumscribed by the reflection of the anhistous membrane, that the 

 villi of the chorion can allow any vessels to be developed. 



422. The chorion is met with in all the vertebral animals; but 

 with such modifications that most physiologists have been unable as 

 yet to agree concerning its nature: in the batracian reptiles, as in 

 women, it forms the covering of the ovule; in the saurians it ex- 

 hibits a much greater thickness and solidity, although it has the same 

 relations with the organs of the female. In the ophidians it com- 

 poses that membrane which is so dense and difficult to break, and 

 which constitutes the shell or outer covering. In birds the chorion 

 is much farther removed from the vitellus, and in. fact is not formed 

 until after several other lamince. This is .the membrane that lines 

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