THE VEINS. ’ 417 
opposite the head of the tibia this bifurcates into the anferior and 
posterior tibial arteries. Just after emerging from the pelvis it gives 
off a considerable branch, profunda femoris, then the epigastric ; and in 
running down through the muscles of the thigh it gives off numerous 
small branches to them. 
THE VEINS. 
THE VEINS generally correspond with the arteries, the blood of which 
they return to the heart. Thus there is a large vein which conveys all 
the blood from the anterior half of the body supplied by the anterior 
aorta, and this is called vena cava anterior. In a similar manner the 
posterior vena cava is made up of veins which accompany the several 
arteries that are found throughout the body, with one remarkable ex- 
ception connected with the secretion of bile. If the splenic and mesen- 
teric veins are traced they will be found to unite together into a large 
trunk, which, instead of going on to empty itself into the vena cava 
posterior, enters the liver, where it is called the vena porte, and branches 
out again like an artery, the general purposes of which it serves by 
furnishing blood for the secretion of bile. This will be more fully 
described under the head of the liver, in the next chapter. From the 
terminations of the portal veins and hepatic artery the hepatic veins arise, 
and these empty themselves into the posterior vena cava, just behind 
the diaphragm. JBesides that brought by the two vene cave, the blood 
from the heart itself enters the auricle through the coronary veins. 
ALTHOUGH, IN GENERAL, the veins and arteries correspond in their rami- 
fications, yet there is a large class of superficial veins which are not 
accompanied by any of the latter vessels. In horses which for many 
generations have been accustomed to fast work, these superficial veins 
are strongly developed, and are particularly plain in the Arab and his 
descendants. As a consequence of this, and of the fact that many of the 
arteries are accompanied by two veins, the whole number of veins is much 
greater than that of the arteries, and the internal area of the former may 
be considered to be nearly double that of the latter. In their walls the 
veins are much thinner than the arteries, though like them they have 
three coats, the serous and cellular being very similar in structure, but the 
fibrous is very much thinner and devoid of muscular fibres. A feature 
peculiar to the veins is the existence of valves, which are sometimes 
single, at others double, and occasionally arranged in threes and fours 
azcund the interior of the large veins. They vary in numbers, and are 
altogether absent in the pulmonary veins, in the vene cave, and the 
vena porte. 
THE ANTERIOR VENA CAVA is made up of the jugular vein, the pectoral, 
vertebral, axillary, and cervical veins, and the vena azygos. The jugular 
vein, which is that usually selected for bleeding, returns the blood from the 
brain, jaws, and neck, along each side of which it lies, separated from the 
carotid artery in the upper part of the neck by a layer of oblique fibres 
belonging to the levator humeri. In the lower half the vein becomes 
more deeply seated, approaches more closely the carotid artery, and, 
entering the chest with it, falls into the vena cava anterior between the 
first and second ribs. Near its termination it receives the superficial 
brachial vein (the plate vein), which passes up in front of the arm, along 
the anterior edge of the flexor, and winding upwards in the hollow 
between the arm and sternum joins the jugular vein. The vertebral 
EE 
