282 RICHARD E. SCAMMON 



HISTORY OF THE HEPATIC SINUSOIDS 



The sinusoids of the selachian Hver are most striking objects 

 and at one time form decidedly more than half of the entire bulk 

 of the organ. Minot ('00) has given the only description of them 

 which is at all complete as a part of his exposition of the nature 

 of the sinusoidal circulation. Brief notes are also to be found 

 in the papers of Holm ('97) and Debeyre ('09). The general 

 development of the veins of the liver in these fishes has been 

 studied by Rabl ('92), Hoffmann ('93) and Hochstetter ('93). 

 The early development of the omphalo-mesenteric veins has 

 been observed in detail by Mayer ('87) and by Ruckert ('88). 

 Therefore I shall give only the briefest outline of the general 

 history of the veins, and will begin with the conditions found in 

 Acanthias embryos from 8 to 10 mm. in length. In such embryos 

 there are paired omphalo-mesenteric veins extending forward 

 to the sinus venosus on either side of the gut. The left vein is 

 somewhat larger than the right. At first the right and left 

 trunks are quite separate but soon they form two anastomoses, 

 one posterior to the pancreas and the other, a little later, just 

 posterior to the liver below the foregut. From the latter anasto- 

 mosis the veins pass forward on eithei' side of the foregut and 

 medial to the. lateral hepatic pouches until they reach the anterior 

 end of the liver where they join and form the sinus venosus. 

 It is important to note that in Acanthias in early stages only the 

 medial surfaces of the lateral pouches are in contact with vascular 

 channels. There are no vascular channels between the lateral 

 surfaces of the hepatic pouches and the mesothelium covering 

 them. 



Figure 11 A shows a reconstruction of a somewhat later stage 

 in which important changes have taken place. Now only the 

 left omphalo-mesenteric vein passes through the groove between 

 foregut and lateral hepatic pouch to join the sinus venosus. The 

 right vessel ends blindly anteriorly and is connected with the left 

 by the large anastomosis which lies behind the liver. In the 

 meantime either a single vessel or several vascular sprigs have 

 grown back on either side from the sinus venosus and passing 



