DEVELOPMENT OF TROBORCIDTA. 741 



and at each pole of the elongated sac, by the subcircular villous 

 patch. The umbilical cord, f, formed by one venous and two 

 arterial trunks, and by the slender neck of the allantois, g, with 

 the connecting cellular tissue and the covering of amnios, is short 

 and somewhat flattened. It measured about 6 inches in length, 

 before the division of the vascular trunk, and about 3 inches in 

 circumference. The inner surface of the amnios is roughened by 

 brownish hemispherical granules, from 1 line to y^-th of a line 

 in size, commonly about half a line ; the outer surface is finely 

 wrinkled, but smooth. The bag formed by the mucous or un- 

 vascular layer of the allantois is of considerable size, is continued 

 from the base of the umbilical cord, so expanding between the 

 chorion and amnios as to prevent any part of the amnios attaining 

 the inner surface of the placenta. The allantois divides, where 

 the amnios begins to be reflected upon it, into three sacculi : one 

 extends over the inner surface of the annular placenta, and a 

 little way into one end of the chorion : a second extends into the 

 opposite end of the chorion, a '; it there bends round toward the 

 placenta, and its apex adheres at that part to the first division of 

 the allantois : the third prolongation subdivides into two smaller 

 cavities, each terminating in a cul-de-sac, encompassing, and 

 closely attached to, the primary divisions of the umbilical vessels. 

 The line of adhesion of the amnios to the allantois, where it is 

 reflected upon these cul-de-sacs, measures 3 feet 6 inches. 



The primary branches of the umbilical arteries and vein diverge 



^ 



from the umbilical cord in four divisions : they reach, first, the 

 borders of the placenta, and then ramify in its substance and upon 

 the inner surface of the chorion, being supported there, and more 

 or less surrounded, by the layer of the allantois called ( endo- 

 chorion.' Upon the endochorionic vessels are developed a number 

 of flattened, oval, or subcircular bodies, e, e, of a compact, struc- 

 tureless tissue, varying in diameter from an inch or more to half a 

 line. On separating the chorion from the allantois, these bodies 

 were found to belong entirelv to the latter membrane : the vessels 



^J V 



upon which they seem to be developed pass on their chorionic 

 side, the bodies adhering to the allantoic side of the sheath of the 

 vessel : they are most abundant near the placenta, and become 

 wider apart as they approach the poles of the chorion : 1 counted 

 120 : the smaller ones occur on the free duplicatures of the 

 allantois continued from the umbilical trunks : in almost every 

 case they are developed on the course of the large vessels, and 

 are restricted, with few exceptions, to that part of the allantois 

 which is in contact with the chorion. Their free surface is 



