252 



EMBRYOLOGY. 



and, as it were, surrounded them with a sheath (amniotic sheath). 

 The structure thus produced, the umbilical cord, f uniculus umbilicalis, 

 is now the only means of connection between the embryo, which 

 floats free in the amniotic fluid, and the wall of the blastodernric 

 vesicle. Its attachment to the latter always coincides with the place 

 where the placenta is developed. 



By the enlargement of the amnion the umbilical vesicle is crowded 

 out to the surface of the blastodermic vesicle, where it is enclosed 

 between amnion (am) and chorion (ch), at some distance from the 

 place where the umbilical cord is attached. It continues to exist 

 here up to the time of birth, although in a very rudimentary condition. 

 It is only by painstaking examination that it is to be found, usually 



several inches away from the 



GI.U --nOr7nnf~l/If~irir~ margin of the placenta. Its 



longest diameter measures only 

 from 3 to 10 millimetres. It 

 was on this account that the 

 older text-books of anatomy, 

 physiology, and embryology 

 contained the statement 

 that in Man the vesicula 

 umbilicalis disappeared as a 

 useless structure ; this idea 

 prevailed until the constancy 

 of its presence was demon- 

 strated by B. SCHULTZE. 



M - 



Fig. 145. Cross section through the mucous mem- 

 brane of the uterus, after KUNDRAT UND ENGEL- 



MANN. 



Gl.u, Uterine glands ; M, muscular layer of the 

 uterus. 



4. The Deciduae. 



The deciduce or caducous 



foetal membranes take their origin from the mucous membrane of the 

 uterus, the structure of which is greatly altered during pregnancy. 



In the unmodified condition the mucous membrane is a soft layer 

 about a millimetre thick, which reposes directly and immovably upon 

 the musculature (M ) of the uterus, which does not possess a submucosa 

 in this region (fig. 145). It is traversed by numerous tubular uterine 

 glands (glandulse utriculares, Gl.u), which begin at the surface with 

 small orifices and pass directly downward in a sinuous course close 

 to one another until they reach the musculature (M), where they 

 terminate, often after dichotomous division. 



Mucous membrane and glands are lined with ciliate cylindrical cells. 

 The connective tissue that separates the glands embraces an extra- 



