OF THE HUMAN UMBILICAL CORD AND PLACENTA. 353 



For the duplicatures of veins and arteries contained in the terminal villi are 

 surrounded, as was first shown by Mr Goodsir in one of his admirable papers on 

 the placenta, by a thin layer of nucleated cells, probably, as he suggests, for the 

 functions of nutrition and respiration. This new layer of tissue is apparently 

 derived from the decidua or hypertrophied mucous membrane of the uterus, and, 

 along with the lining membrane of the maternal vascular system of the placental 

 blood-cells, constitutes the maternal portion of the human placenta ; but neither 

 nerves nor capillaries have been traced into these structures. 



The mode or modes of nourishment and growth of a structure like the um- 

 bilical cord and placenta, presenting no capillaries nor vasa vasonim, constitutes 

 an interesting problem in physiology ; but my remarks are at present limited to 

 peculiarities in the mere anatomical type of these parts. These anatomical 

 peculiarities, to which I have attempted to draw the attention of the Society, 

 may in conclusion be summed up as follows : — 



1. The volume of the umbilical cord and foetal portion of the placenta is 

 formed of nucleated cellular tissue, traversed by the tubes of the umbilical 

 arteries and vein and their numerous placental subdivisions, and invested by a 

 sheath of serous membrane. 



2. Into the composition of these parts, no capillaries, vasa vasorum, lym- 

 phatics, nor nerves, are found to enter. 



3. Hence, in human anatomy, we have these organs, forming a large mass, 

 weighing on an average about two pounds, presenting a type of structure re- 

 sembling that of some of the inferior zoophytes. And, 



4. The human mother and her child, two of the most highly organised beings 

 in existence, are thus temporarily united together, during the intra-uterine life of 

 the latter, by structures of the lowest zoological type. 



VOL. XXTII. PART II. 5 D 



