The blood vessels are very numerous in this system; they are found in it even in greater proportion than in the other; more blood consequently penetrates them. This fact is remarkable, especially in the intestines, in which the mesenteric arteries distribute numerous branches, over an extremely delicate fleshy surface. But I would remark that this appearance is to a certain degree deceptive, as many of these vessels only traverse the fleshy surface to go to the mucous membrane. In the ordinary state they give to the gastric viscera a reddish tinge, which I have rendered at will livid and afterwards brought back to its primitive state, by shutting and afterwards opening the stop-cock adapted to the wind pipe, in my experiments upon asphyxia.
The absorbents and exhalants have nothing peculiar in this system.
The nerves come to them from two sources; 1st, from the cerebral system; 2d, from that of the ganglions.
Except in the stomach in which the par vagum is distributed, the nerves of the ganglions predominate everywhere. In the heart, they are the principal; in the intestines, they are the only ones; at the extremity of the rectum and the bladder, their proportion is greater than that of the nerves coming from the spine.
The cerebral nerves intermix with them, in penetrating the organic muscles. The cardiac, solar, hypogastric, plexuses, &c. result from this intermixture which appears to have an influence upon the motions, though we are ignorant of the nature of this influence.
All the nerves of the ganglions which go to the organic muscles, do not appear to be exclusively destined to them. A great number of filaments belong only to the arteries; such is in fact their interlacing, that they form, as we have seen, around these vessels a real nervous membrane, superadded to their own, and exclusively destined to them. I would compare this nervous envelope to the cellular envelope which is also found around the arteries, and which is wholly distinct from the surrounding cellular texture; thus it only has communications with the nerves of the organic muscles, without being distributed to these muscles. Besides as the nerves of the ganglions are always the most numerous and essential in them, and as their tenuity is extreme, the nervous mass destined to each is infinitely inferior to that which is found in the voluntary muscles. The heart and the deltoid muscle compared together, exhibit in this respect a remarkable difference.
ARTICLE THIRD.
PROPERTIES OF THE MUSCULAR SYSTEM OF ORGANIC LIFE.
Under the relation of properties, this system is in part analogous to the preceding, and in part very different from it.