<;HAN(;Eri IN FETAL VESSELS OF THE LIVER 513 



similar adventitia. But no part of the hypogastric arteries 

 except the distal portions were found wholly without longitudinal 

 muscle fibers. However, the longitudinal layer varied greatly in 

 thickness and distribution. This variation in thickness Lochman 

 ascribed to the differences in contraction of the vessel in man. 

 Most of the longitudinal fibers lay internally near the endothelium 

 but various-sized bundles were found scattered about irregularly 

 in the innermost portions of the circularis and not infrequentl}^ 

 good-sized bundles were also found in the outer layers. In 

 addition to this peculiarity in distribution of the longitudinal 

 fibers, a peculiar, coarse radial striation or better lamination as 



Fig. 24 Trau8veirie .section of the hypogastric artery of a new born lamb, show- 

 ing the radial striation of the circularis. A, circularis, B, longitudinalis. X97. 



shown in figure 24 was occasionally seen in the circularis of the 

 arteries but never in that of the vein. This striation which was 

 not present in all portions of the cross-sections was due to local 

 accumulations of loosely-arranged circularly-disposed bundles of 

 muscle fibers. Since these local accumulations lay approximately 

 opposite each other they gave rise to the above mentioned coarse 

 radial striations. Moreover, the fibers of the circularis were 

 usually rather loosely disposed and the concentric strands sepa- 

 rated from each other by a fine collaginous fibrous tissue. 



The lumina of the arteries as in case of the paired portions 

 of the uml)ilical veins, were roughly stellate. This characteristic 



