rvf wViipli 



CONNECTIVE TISSUE. 



151 



of which is deposited the jelly-like "intercellular" substance. In 

 this substance globular and isolated cells occur. Virchow found 

 that, besides the three main blood-vessels (two arteries carrying- 

 venous blood, and one vein carrying arterial blood), there are no 

 other vessels throughout the entire length of the umbilical cord. 

 Capillaries exist only at a short distance (about one-half inch) 

 close above the insertion of the cord into the abdominal wall. 

 Virchow draws attention to the heavy coats of the vessels, the 

 muscular character of which was discovered afterward by 

 Kolliker, and concludes that these coats play an important part 

 in the occlusion of the vessels whenever they are severed or torn, 



FIG. 51. SEGMENT OF THE UMBILICAL CORD OF A HUMAN EMBRYO. 

 FOUR MONTHS OLD, IN TRANSVERSE SECTION. 



A , artery ; V, vein ; M, myxomatous tissue, the common adventitia ; E, epithelial cover. 

 Magnified 25 diameters. 



without ligature. The mucous tissue, Virchow * says, is attached 

 to the imperfectly developed adventitial coat of the three vessels. 

 In my conception the umbilical cord in toto is the adventitial 

 coat, common to the three blood-vessels, of which the vein, as a 

 rule, has a much narrower muscle-coat than the two arteries. 

 (See Fig. 51.) No capillary blood-vessels and no lymphatics have 

 been discovered in this tissue, neither is anything certain in re- 

 gard to nerves, though it is probable that the three vessels are 



* "DieCellularpathologie." Vierte Auflage. Berlin, 1871. 



