OP THE VEINS. 295 



system is comprehended in the general venous system, espe- 

 cially on account of the nature of the blood it contains. 



442. In the vertebrated oviparous animals another venous 

 system, analogous to the intestino-hepatic vessels, is found. 

 This particular system* is formed by the union of the veins 

 of the middle region of the body only, or of this region and 

 of the tail, which veins terminate in the kidneys in the same 

 manner as the arteries, sending sometimes a branch to the 

 vena porta, that is lo say, to the liver. I have sometimes ob- 

 served, in the dog, the vena porta to have one or two renal 

 terminations. 



443. The number of veins is in general greater than that 

 of the arteries. There are two venae cavae, and one cardiac 

 vein to correspond with the single trunk of the aorta. There 

 are, in the same manner, four pulmonary veins to correspond 

 with the single pulmonary artery and its two branches. But 

 each of these venous divisions corresponds with a branch of a 

 corresponding artery. In almost the whole extent of the body, 

 there are many more subcutaneous veins than arteries, and in 

 deep seated parts, there are almost every where two venae 

 committes for a single artery. In the stomach, the spleen, the 

 kidneys, the testicles, the ovaries, and some other parts, the 

 number of veins is equal to that of the arteries. In some 

 parts, the number of veins is even less than that of the arte- 

 ries, as for instance, in the umbilical cord, in the penis, in the 

 clitoris, in the gall-bladder, surrenal capsules, &c. But this 

 is compensated by the difference of capacity. The size of the 

 veins generally, is in fact more considerable than that of cor- 

 responding arteries. 



The sum of the veins, or their total capacity, is then greater 

 than that of the arteries. Many calculations have been made 

 respecting it; but we can only say with Haller, that the veins 

 are at the least double of the arteries in capacity. But, indepen- 

 dently of individual, accidental, or temporary differences, and 

 those which depend upon the kind of death, it continually 



* Lud. Jacobson, de systematc venoso peculiuri in pcrmultis animalibus 

 vbservato. Hafnije, 1821. 

 39 



