62 
OK THE PHYSIOOKOMY OF SEEPEKTS. 
disappears at the extremity of the tail, supplying in its 
course the neighbouring organs. After giving off the in- 
tercostal arteries, it sends branches to the stomach, the liver, 
the organs of generation, and to the kidneys. The mesen- 
teric artery arises opposite to the pylorus, and several other 
branches are distributed on the intestines. The right aorta, 
before descending behind the heart, sends a considerable 
branch to the head, which is named by Cuvier the artery 
of the neck,^ This branch, after furnishing the intercostal 
arteries to the neck, perforates the flexor muscles of the 
head, where it is lost. The carotids arise from the trunk 
of the right aorta near its base ; they extend along the 
oesophagus, towards the head, into which they penetrate, 
after being divided into numerous branches, which supply 
blood to the organs within the head. This disposition of 
the carotids, described from the Boa constrictor, is by no 
means the same in all other serpents, which, in general, 
have only one carotid, I that on the left side : this artery 
alone furnishes the whole blood to the head. The carotids 
send a small branch to the thyroid gland, and other branches 
to other organs inclosed in the cavity of the neck. Two 
jugular veins, adherent to the carotids, descend along the 
oesophagus, carrying back the blood from the head to the 
heart. I have observed in a Boa constrictor three unequal 
veins preceding the vertebral column ; the first, near the 
head ; the second, about the middle of the neck ; the third, 
in the abdominal region. It is evident that to reach the 
heart, the latter rises up, whilst the others descend. The 
vein, which carries back the blood from the posterior parts 
of the animal, divides to form the two renal veins, which 
pass along the whole length of the interior surface of the 
kidneys, from which they receive a great many branches : 
after having given rise to a vena cava, the branch of the 
right side unites to that of the left side to form a large 
vein. This is the inferior cava, which penetrates among the 
parenchymatous substance of the liver, to receive the blood 
brought by the vena portae, in passing out of the superior 
* Arteria Vertebralis, Schlemm, i. 1. 
t The artere carotide commune of Cuvier ; arteria cephalica of 
SCHLEMM. 
