THE POSTERIOR VENA CAVA. 711 



metatarsus, it communicates, by a short, thick branch, with the deep vein. It 

 then continues its ascending course by entering the tarsal sheath along with the 

 plantar arteries, and is prolonged in the hollow of the hock, passing along the 

 femoro-popliteal nerve, forming the posterior root of the internal saphena. 



C. Deep Metatarsal Vein. — This is placed beneath the suspensory liga- 

 ment, at the inner side of the principal interosseous plantar artery. Near the 

 tarsus, it receives a very large branch from the external vein, and then passes 

 through the cuboido-cuneo-scaphoid canal, to form the largest root of the anterior 

 tibial vein. 



8. Veins of the Digital Region. 



As these resemble, in every respect, those belonging to the anterior limb, the 

 same description will suffice for both (see p. 698). 



Differential Characters in the Veins of the other Animals. 

 It does not come within our plan to give a complete description of the venous system in 

 these animals, because of the small utility of such a study. To remain faithful to our object, 

 we confine ourselves to tlie indication of the special characters of the veins on which 

 bleeding is usually practised, and those which may be interesting in a surgical point of view — 

 such as tlie digital veins of Ruminants. 



A. Angular Vein of the Eye. — This vessel is remarkable for its large volume in the 

 Sheep ; and as it is well defined beneath the skin, in consequence of the fineness of that 

 meml>rane, it is more frequently selected for phlebotomy than in other animals. 



B. Jugular Vein. — Very large in all animals, and particularly in the Ox, this vein 

 deserves the preference given to it when it is proposed to abstract a certain quantity of blood 

 from the system. 



In all non-soliped animals there is found an accessory jugular, which sometimes exists in 

 tlie Horse — but is much less in size — alongside the common carotid artery. It arises from the 

 occipital vein, and therefore extends the whole length of the neck. Sometimes its diameter 

 is small; but it is often so large as to receive a very notable quantity of blood from the 

 principal jugular, when compression is applied to the latter to favour the flow of blood after 

 opening it — a circumstance that explains the difliculty sometimes experienced in obtaining a 

 voluminous jet of blood. 



C. Abdominal Subcutaneous Vein.— In the Bovine species, this vessel has an enor- 

 mous volume, especially in the Milch-cow, in contradistinction to the subcutaneous thoracic 

 vein, which is always very small. 



This vein is prolonged forward on the wall of the abdomen, to near the xiphoid cartilage, 

 where it passes through to join the internal thoracic vein.' Behind, it is formed by multiple 

 branches, which anastomose with each other, or with those of the opposite vein, and are in 

 communication with the proper external pudic veins. 



D. Internal Saphena Vein. — This is always smaller than in Solipeds, and is rarely 

 selected to extract blood_from. 



E. External Saphena Vein.— This vessel is, on the contrary, more voluminous than in 

 the Horse, and at the same time more superficial ; consequently, it is more favourably situated 

 for phlebotomy, as well in Pigs and the Carnivora, as in Ruminants. It arises from the union, 

 in the hollow of the hock, of the two principal roots furnished by the metatarsal veins. 



F. Veins of the Posterior Foot in the Ox. — As in the Horse, they commence in the 

 subungual network of the digital region, which is double, like the region itself. 



a. Three digital veins leave this reticulum : 1. A median or anterior one, arising by two 

 roots from the anterior part of each network, passing between the two digits, and joining the 

 anterior .superficial metatarsal vein above the fetlock. 2. Two laterals, communicating with 

 one another, behind, by a transverse anastomosis which receives several venules from the 

 ungual plexus, and with the anterior vein by an iuterdigital branch, united by an arch in front 

 of the flexor tendons, above the sesamoid groove. 



b. These digital veins are continued by five metatarsal veins : two deep and one superficial 

 anterior, and two posterior. 



' The openings through which these vessels pass in the abdominal parietes, are commonly 

 named the milk fountains or doors. 



