I have many times injected the veins of the muscles of animal life with ease, from the trunks towards the branches, which makes me believe, notwithstanding what Haller has said, that in these organs, as in the heart, the valves are less numerous than in many others. No doubt the assistance the veins derive from their surrounding organs supplies the place of these folds, or rather renders them useless, the weight of the column of blood not making a great effort against the venous parietes. The varices of the muscular veins are, as we know, extremely rare. These veins are of two orders; one accompanies the arteries and follows the same course, the others are spread superficially on the surface of the organ, without having corresponding arteries. There are absorbents and exhalants in the muscles; but we can with difficulty trace the first, and the second cannot be perceived. _Nerves._ Almost all the nerves of the muscles of animal life come from the brain; the ganglions furnish a few of them; when this happens, as in the neck, the pelvis, &c. besides the filaments coming from these nervous centres, there are always filaments of cerebral nerves; without this, these muscles would be involuntary. Few organs receive more nerves in proportion to their size than the muscles. In general the extensors appear to have rather fewer than the flexors; but the difference is trifling. It is true that all the great nervous trunks are in the direction of flexion, that in that of extension there are only branches, as we see in the posterior part of the arm, of the fore-arm, the vertebral column, &c. It is true also that this remark is likewise applicable to the existence of the vessels, which are larger and more numerous in the first than in the second direction; but this greater number of vessels and nerves arises from this, that there are many more flexors than extensors, that the first are stronger and have more numerous fibres; so that each of these fibres hardly receives more nervous or vascular filaments in one kind of muscles than in the other. I think that there is but little foundation for what has been said upon the difference of the strength of the fibres of the flexors and of the extensors, upon the predominance of the first, &c. If these are superior, it is either because they are more numerous, as in the foot, the hand, &c. or more advantageously arranged, as in the trunk on which the abdominal muscles act very far from the point of attachment to bend the spine, whilst to extend it, the dorsal muscles exert their action immediately at the side of this point of attachment, as also in the neck, where the muscles that draw down the lower jaw and head when this bone is fixed, are much further from the occipital condyles, than the muscles which produce extension. Whatever may be the cause of the superiority of the flexors, the fact cannot be doubted. 1st. In hysterical convulsions, in those of infants, in all the spasmodic