158 APPENDAGES OF THE FCETUS. 



men, and they were so far right, that it has no where been found 

 possessed of the same characters it exhibits in the human species; 

 but if, laying aside the idea of a complete analogy, we are content 

 to seek for its elements, more or less modified in other vertebral 

 animals, we soon perceive that it is in almost all of them replaced 

 by a coat which is equally inorganic. Thus, in the ophidian rep- 

 tiles its analogue is a simple mucous imhiitus; in the batracians it 

 is represented by a similar but much thicker layer; in birds, not- 

 withstanding what M. Dutrochet has said, the calcareous shell is its 

 substitute, and as M. Cuvier has already maintained; lasUy, in 

 almost every species of the mammiferse there is to be found a lamella 

 on the external surface of the chorion, which is sometimes nearly 

 fluid, at others pretty consis:ent, and of a considerable thickness, of 

 a greenish or yellowish color, and which serves as a caduca. 



§. II. Proper Membranes of the Oviini. 



A. Of the Chorion. 



412. To prevent, for the future, the chorion from being con- 

 founded with any other membrane, it will suffice to remember what 

 I have just said concerning the caducous membrane, and that it 

 constitutes the first organised or solid tunic of the ovum as we pass 

 from the womb to the foetus, and the second in proceeding from the 

 foetus to the womb. 



413. Primitive condition. In a production of ten or twelve days 

 standing, the chorion presents the appearance of a velvet-like hyda- 

 tid, or a small transparent vesicle; its external surface, free from all 

 adhesions, is somewhat fungous or fretted throughout its whole ex- 

 tent; its interior is filled with a clear serous fluid. 



414. In products of three or four weeks, the chorion is not smooth 

 on both its surfaces, as has been erroneously slated by a multitude 

 of commendable writers. I have never, whatever care I may have 

 taken, seen it smooth exteriorly, nor velvety internally. \ At a fort- 

 night, at three weeks, at one month as well as at two, 1 have always 

 found its external surface covered with the same down, its internal 

 surface even and polished, and its transparency neither more nor 

 less decided than at any other period of gestation. 



415. Granulations, and villosities. It is generally thought that 

 the down that covers the chorion is of a vascular nature; but as early 

 as 1823 I ventured to oppose this hypothesis. What proves that the 

 filaments of the chorion are not vessels is this, that they are to be 

 seen before blood vessels of the cord are recognisable. Besides, until 

 the sixth week, every flock is at least as large as one of the umbilical 



