THE ANTERIOR VENA CAVA. 613 



" The general disposition of the venous canals in the texture of the 

 reticulum supporting them, closely resembles that of the secondary ribs of 

 the limb (or laminar merithal) of certain asymmetrical leaves. In their 

 course they follow an irregularly-broken line, intercepting each other by 

 joining at short intervals, so as to form unequal-sized, unsymmetric, 

 polygonal spaces. 



" These venous conduits have a double canal for discharging themselves : 

 a central, the least considerable and least constant ; the other peripheral 

 or circumflex, corresponding to the artery of the same name, 1 and whose 

 satellite vein it is. 



** Central canal. The central canal is formed by the simultaneous 

 anastomoses of a crowd of venous ramifications converging towards the 

 centre of the digit. It is of a parabolic shape, and embraces in the concavity 

 of its curvature the point of the pyramidal body, whence it throws its two 

 branches in a parallel manner on the sides of that body, into the bottom of 

 the lateral lacunae as far as the cartilaginous bulbs, where it proceeds 

 to the external coronary plexus. This disposition is not constant, however, 

 as specimens are frequently met with in which this central canal is replaced 

 by multiple veins, which are more considerable than those forming the 

 whole of the plexus, and which serve them as overfalls towards the super- 

 ficial coronary plexus. 



Circumflex vein, or peripheral venous canal. " This vein is of large 

 calibre, and formed by divergent ramifications from the solar plexus, as well 

 as the descending veins of the podophyllous plexus ; it margins the external 

 limb of the villous tissue in following a slightly undulous line within the 

 circumflex artery, whose satellite it is. It is sometimes broken up, at 

 certain points of its course, into several smaller canals which are continuous 

 with its trunks. 



" In its circular route, all the divergent solar and descending podo- 

 phyllous veins are discharged into it, and it terminates, at the extremities of 

 the crescent formed by the third phalanx, in several large branches which 

 pass beneath the podophyllous tissue to the lateral cartilage, where they 

 concur to form the superficial coronary plexus. 



" B. PODOPHYLLOUS VENOUS PLEXUS OR NETWORK. The veins of the 

 podophyllous plexus exhibit a disposition analogous to those of the solar 

 plexus ; like them, they are sustained in the meshes of a fibrous texture (the 

 reticulum processigerum of Bracy Clark, the subpodophyllous reticulum ot 

 French Veterinarians) spread on the anterior surface of the bone, in the 

 same way as the periosteum is on other bones, and continuous with the 

 corium of the laminal tissue. Communicating largely between each other 

 by multiple anastomoses, like the solar plexus, they appear to be completely 

 isolated from the deeper parts, from which it is commonly believed they 

 emanate. 



" Tortuous and split up into branches in their course, the podophyllous 

 veins wind in a serpentine manner along the length of the laminsB they cover, 

 very close to each other, and forming narrow elongated meshes. Their 

 confluence is such, that at certain points they appear bound together by their 

 external walls. 



" The calibre of these vessels is tolerably uniform throughout the extent 

 of the podophyllous plexus, except towards the posterior parts, where their 

 principal canals empty themselves into the coronary plexus. 



" The podophyllous veins are in anastomotic communication, below, with 



1 The inferior circumflex artery of the foot. 

 42 



