Anatomy of the Umbilical Cord. 423 



epithelial surfaces, nor do I think that there is much difference in their 

 function. 



The epithelial covering of the cord is said to be derived from the 

 amnion ; but this is a loose method of description which has yet to be 

 substantiated. 



In all the microscopic examinations from which descriptions are taken 

 in this paper, the sections have been made by my freezing section cutter, 

 from fresh tissue unless otherwise stated ; and they have been submitted 

 to various staining-processes by the action of litmus, hsematoxylin, red 

 cabbage, &c, as described in Humphrey and Turner's 'Journal of Anatomy 

 and Physiology/ May 1875. The lenses used have been a half-inch and 

 a quarter-inch objectives of Natchet, with the corresponding eyepieces 

 1, 2, and 3, and an immersion sixteenth of Hartnack. 



To obtain pieces of the epithelial surface of the fresh cord of any size 

 and of sufficient thinness to see the surface transparently was a matter 

 of considerable difficulty. I first of all tried freezing the fresh cord 

 while pressed flat against a piece of glass, tearing off the glass and then 

 cutting off the flattened surface. To the fact that the glass removed 

 with it a great part of the epithelium I owe a most important though 

 accidental observation. I further found that first smearing the glass 

 with glycerine prevented the cord becoming intimately attached to it ; and 

 by carefully washing off the glycerine by distilled water I obtained a 

 perfect epithelial surface free from disturbance. This I examined after 

 being treated in various ways. Soaking the section in an ammoniated 

 solution of litmus or hseniatoxylin and reducing the colour by washing it 

 in a -004 per cent, solution of nitric acid, I found that the epithelial 

 layer was single and composed of irregularly polygonal cells, regularly 

 nucleated. These cells were bedded in a fibrillar matrix, very thin, and 

 in which no special structure could be discovered, and which is certainly 

 only a slightly condensed arrangement of the canalicular system on which 

 the cells lie. Virchow has described the subepithelial tissue as a " some- 

 what denser dermoid layer ; " but I have failed to see any such analogy. 

 The fusiform nuclei of the canalicular tissue are to be seen (Plate 11. 

 fig. 6) immediately under the single layer of epithelium, lying in the direc- 

 tion of the long axis of the cord. These epithelial cells differ from similar 

 cells on the foetal surface of the placenta and amnion only in being some- 

 what less regular in size and arrangement ; and, indeed, in these points 

 they differ to a considerable extent on various parts of the cord itself, for 

 they are slightly larger and more regular near the foetus than near the 

 placenta. That there is only a single layer of cells is a point on which 

 I am satisfied ; for I have stained the whole layer removed on the glass, 

 as I described above, and I have never been able to focus one cell above 

 another. 



.Further, in a microscopic section of a fresh cord stained with hsema- 

 toxylin the epithelial covering may be seen to be turned over. The 



