350 PROFESSOR SIMPSON ON THE ANATOMICAL TYPE OF STRUCTURE 



united together by structures of the lowest type of zoological organisation. That 

 the structures which connect the mother and child in utero, viz. the umbilical 

 cord and placenta, are of such a low type of organisation as I allude to, the fol- 

 lowing observations will tend to show. 



Let us begin with the type of structure of the umbilical cord. 



The rope-like formation constituting the funis uinbilicaUs is generally stated 

 to consist in the latter periods of pregnancy of the following component parts, 

 viz. : — 



1st, Of one umbilical vein. 



2d, Of two umbilical arteries. 



^d, Of cellular or areolar tissue surrounding these vascular tubes, and con- 

 taining in its meshes the so-called gelatine of Wharton ; and 



Ath, Of a single enclosing sheath, formed by an extension of the amnion. 



At an early period of pregnancy, other structures are included in the umbili- 

 cal cord, as the vitellary and allantoid ducts, and the omphalo-mesenteric vessels ; 

 but these are not connected with our inquiry, and nothing, at the most, but very 

 shrivelled remnants of them remain in the fully-developed cord. 



In relation to the subject of our present inquiry, it is of more importance to 

 mark the interesting fact, that though by many of our greatest and best anatomists 

 the finest injections have been often thrown into the umbilical vessels, both 

 arteries and veins, no capillaries have ever thus, or otherwise, been traced in any 

 of the component tissues of these tubes. No vasa vasorum have ever been de- 

 tected in the walls or structures of the umbilical arteries or veins. On this point, 

 one of the latest and most careful anatomists who has written on the " Forma- 

 tion and Circulation of the Human Placenta," viz.. Professor Schroeder Van 

 DER KoLK of Utrecht, observes as follows : — " That the umbilical cord has no 

 smaller capillaries besides the large umbilical vessels, is universally accepted. 

 Whether this opinion be grounded on a careful examination, I know not ; but it 

 appeared to me sufficiently important to make it an object of particular inquiry. 

 By filling with sufficient force the umbilical vessels with very fine injection 

 matter, so that the vasa vasorum, if any be present, must also be filled, I saw, 

 after the cord was dried, moistened with turpentine, and examined under the 

 microscope, that nowhere was there a trace of any vasa vasorum, so that the 

 umbilical cord contains the only example of blood-vessels which receive no vasa 

 vasorum. After an examination for this very purpose, I could as little discover 

 them in umbilical cords in the third month of pregnancy as in others after 

 pregnancy had been perfect." 



The statement that the umbilical cord contains in its structure no capillary 

 vessels, or even any vasa vasorum, requires to be qualified with one remark, viz., 

 that the capillaries and vasa vasorum, which within the body of the foetus extend 

 along the umbilical vessels and abdominal walls up to the umbilical ring, or true 



