264 



dition of the liver is late in its formation and of exceptional occurrence, 

 therefore unimportant. It is due to such an extensive development of 

 connective tissue along the portal canals as leads to their anastomosis. 

 The fundamental characteristic of the liver is its sinusoidal development 

 which accounts for the unusual distribution of connective tissue, the 

 fusion of lobules, and the primitive form of circulation. 



With the development of connective tissue along the bile ducts, 

 an opportunity is afforded for arterial vessels to invade the liver. 

 The coeliac axis early sends out a slender branch which ramifies be- 

 side the portal vein close to the hepatic sinusoids. Connection between 

 this hepatic artery and the sinusoids could not be demonstrated in a 

 rabbit of 29 mm, but it was seen in a cat of 31 mm. The late de- 

 velopment of this vessel in the connective tissue of the liver corre- 

 sponds with the arterial distribution in the adult. The hepatic artery 

 supplies chiefly Glisson's capsule, but some branches following the 

 bile ducts, form capillaries within the liver which empty into adjacent 

 sinusoids (von Ebner). The hepatic artery is always subordinate. 



Wolffian Body. 



A description of the Wolffian sinusoids requires a preliminary 

 account of the posterior cardinal veins, out of which the sinusoids are 

 evolved. "Posterior cardinal vein" is a general term for one of a pair 

 of vessels extending, near the aorta, from the tip of the tail to the duct 

 of CuviER. Each posterior cardinal vein is divisible into three parts ; 

 first, the caudal, extending from the tip of the tail to the Wolffian 

 body; second, the mesonephric, passing along the Wolffian body; 

 and third, the azygos, continuing from the Wolffian body to the duct 

 of CuviER. In the course of development, the mesonephric portion 

 becomes subdivided longitudinally into two vessels, ventro-median and 

 dorso-lateral respectively, between which pass the mesonephric arteries. 

 The ventro-median subdivision lies near the root of the mesentery, 

 from which it receives tributaries. It tends to anastomose, ventral to 

 the aorta, with the corresponding vessel of the opposite side. In the 

 adult it forms a large part of the vena cava inferior '). This vessel has 

 been designated the subcardinal vein. The dorso-lateral sub- 

 division of the mesonephric part of the posterior cardinal vein is as- 

 sociated with the somatic, and generally with the vertebral veins. If 



1) F. T. Lewis, The development of the vena cava inferior. Amer. 

 Journ. of Anat., 1902, Vol. 1, p. 234. 



