62 ON" THE PHYSIOGNOMY OF SERPENTS. 



(lisapjiears 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 tlie 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 tlie right aorta near its base ; they extend along the 

 cesophagus, towards the head, into which they penetrate, 

 after being divided into numerous branches, wliich 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, "f 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 vertebi'ai 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, w^hilst the others descend. The 

 vein, w^iich carries back the blood from the posterior parts 

 of the animal, diiides to form the two renal veins, wiiich 

 pass along the whole length of the interior surface of the 

 kidneys, from which they receive a great many branches : 

 after ha^^ng 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 art ere carotide commune of Cuvier ; arteria cephalica of 

 Schlemm. 



