352 PROFESSOR SIMPSON ON THE ANATOMICAL TYPE OF STRUCTURE 



silver ; and plates of their appearance, when thus injected, were published by him. 

 But it is now, I believe, universally allowed that these mercurial injections were 

 thrown into the areolae of the cellular tissue of the cord, and not into lymphatic 

 vessels ; and I know of no anatomist of the present day who gives credit to the 

 existence of lymphatics in that structure. 



What forms the proper volume of the cord, or, in other words, what forms 

 the material which surrounds the umbilical vessels, and fills up the serous-like 

 sheath of the cord, is usually spoken of as cellular tissue, containing in its 

 delicate meshes a hyaline substance of an albuminoid or mucoid nature, termed 

 the " Gelatine of Wharton." This cellular tissue closely resembles ordinary con- 

 nective tissue, and is composed of nucleated stellate cells or corpuscles. 



The external covering of the cord consists of a serous-like blue membrane or 

 sheath, which, after covering the placenta, envelops the cord from the placenta 

 onwards to the umbilical ring, where, by an abrupt line of division, it meets the 

 white skin of the abdomen of the full-grown foetus. At birth, the contrast at 

 their line of union of the white opaque skin of the foetus with the blue semi- 

 transparent covering of the cord is very striking, and gives in itself the impression 

 of a human cutaneous surface connected organically with a structure of a low 

 zoological type. 



The umbilical cord, as an organic medium of communication between the 

 foetus and mother, is merely as it were a sheath of sarcoid matter perforated 

 with three tubes for the transmission of the foetal blood to and from the placenta ; 

 but it contains apparently no lymphatics, no nerves, no capillaries, not even 

 vasa vasorum. It is skinless, and contained within a sheath of serous membrane. 

 It consists essentially of large nucleated cells formed partly into large and loose 

 cellular tissue containing the gelatine of Wharton, and developed partly into 

 tubal forms, constituting the so-called umbilical arteries and veins. 



The same remarks which apply to the type of structure of the umbilical cord 

 apply to the type of structure of the placenta. 



Into the maternal surface of the placenta no anatomist has hitherto traced the 

 passage of any nervous branches from the applied surface of the uterus, nor have 

 any nutrient arteries been as yet, at least, shown to pass from the uterus into 

 the maternal substance of the human placenta. But at all events, the foetal 

 portion, which remains throughout in some animals distinct from the maternal, 

 is assuredly of the same type of structure as the cord, with one or two points 

 of difference ; for, \st, it contains no gelatine of Wharton ; and, 2d, its vessels, both 

 arteries and veins, divide and sub-divide, till they reach the very small size in 

 which they appear in the terminal villi ; but still neither their coats nor the sur- 

 rounding tissue contain any capillaries or vasa vasorum, or lymphatics, or nerves. 



The enveloping sheath or lining of the terminal villi contains a new arrange- 

 ment of tissue not seen in the umbilical cord or other parts of the placenta. 



