STRUCTUKE OF HUMAN PLACENTA. 449 



the wavy open loop, occur in the flattened and heart-shaped 

 villi. The contorted and other varieties of loops exist in the 

 club-shaped and tuberose villi.* 



Lastly, It must be stated as a fact first recorded and 

 represented by Professor Weber, confirmed by the observations 

 of Mr. John Dalrymple, and to the accuracy of which I can 

 testify, that the same peculiar vessel, or umbilical capillary, 

 may enter and retire from two or more villi before it becomes 

 continuous with a vein. 



6. Of the internal Cells of the Villus. 



Within the internal membrane, and on the external 

 surface of the umbilical capillaries, are cells which I have 

 named the internal cells of the tuft. When the vessels are 

 engorged, these cells are seen with difficulty. When the 

 vessels are moderately distended, and the internal membrane 

 separated from the external cells by moderate pressure, the 

 cells now under consideration come into view. They are best 

 seen in the spaces left between the internal membrane and the 

 retiring angles formed by the coils and loops of the vessels, 

 and in the vacant spaces formed by these loops. These cells are 

 egg-shaped, highly transparent, and are defined by the instru- 

 ment with difficulty ; but their nuclei are easily perceived. 

 They appear to be filled with a transparent highly refractive 

 matter. This system of cells fills the whole space which 



* Mr. Dalrymple, in his paper on the Placenta, in the Med. Chir. Trails., 

 has described with great accuracy the manner in which the foetal vessels ramify 

 and coil in the tufts of the placenta. I am indebted to Mr. Dalrymple for 

 specimens of his injections of the placenta ; and to Dr. John Eeid, for a portion 

 of a placenta injected by Professor "Weber of Leipsic, and have satisfied myself 

 of the accuracy of the descriptions given by these anatomists. My own obser- 

 vations have been made on the unprepared placenta. The drawings of the 

 foetal vessels in Dr. Reid's paper are plans, as the only point he was anxious 

 to establish was, that the villi terminated in blunt extremities unconnected by 

 cellular or other textures, the foetal vessels returning upon themselves. REID, 

 in Edinburgh Medical and Surgical Journal. 



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