VASCULAR SYSTEM
WITH BLACK BLOOD.
The red blood circulates in a single system, the branches of which every where communicate. The black blood on the contrary is contained in two separate systems, which have nothing in common but the form, and which are, 1st, the general system; 2d, the abdominal. We shall now examine the first, and afterwards the second.
The general vascular system with black blood arises as we shall see, from the whole of the great capillary system, is collected towards the heart in great trunks, and terminates in the pulmonary capillaries. As the portion of the heart that belongs to it will be examined hereafter, and the pulmonary artery, by its peculiar membrane, has great analogy with the peculiar membrane of the other arteries, we shall now particularly examine the veins; but we shall describe in a general manner, the common membrane that is spread upon the whole system with black blood.
ARTICLE FIRST.
SITUATION, FORMS, DIVISION AND GENERAL ARRANGEMENT OF THE VASCULAR SYSTEM WITH BLACK BLOOD.
We shall now examine the veins as we have the arteries, in their origin, course and termination. Only we shall do it inversely, to accommodate our ideas to the course in which the blood flows in their channels.
I. Origin of the Veins.
This origin is in the general capillary system. I shall point out in this system, how the veins are continued with the arteries. I would only remark here that these vessels never arise from any organ that the arteries do not enter, as the tendons, the cartilages, the hair, &c.; which evidently proves that the blood is not formed in the general capillary system; it leaves there the principles that made it red, it perhaps acquires there new ones; it is modified in fact, but never created.
It is not as easy to distinguish accurately the veins at their exit from this system, as it is the last arteries at their entrance into it, because the valves prevent injections from penetrating so far. It is in subjects that have died of asphyxia, apoplexy, &c. that the venous ramifications can be best observed. We see then that they are soon divided into two orders; one accompanies the last arteries, the other is distinct from them.