Besides, there is every reason to believe that the ground substance is similar in nature to ordinary protoplasm, but without the granular character commonly but not always exhibited.
Blood-vessels are largely distributed in the substance of a muscle, carrying the materials necessary for its nourishment and chemico-vital changes, and there are also lymphatic vessels as in other vascular parts of the body.
Nerves run through every muscle, by which the muscular contractions are called forth, and a low degree of muscular sensibility is conferred upon the muscular substance.
The blood-vessels of the muscular tissues are extremely abundant, so that when they are successfully filled with a colored injection the fleshy parts of the muscle contrast strongly with its tendons. The arteries, accompanied by their veins, enter the muscle at various points and divide into branches, etc.
The nerves of a voluntary muscle are of considerable size. Their branches pass between the fasciculi and repeatedly unite with each other in form of a plexus, which is for the most part confined to a small part of the length of the muscle, or muscular division, in which it lies.
The voluntary muscles to which distinct names have been given in the system amount to about 240, and they naturally fall under the following four great divisions (the muscles are symmetrical and with few exceptions are in pairs):
| A. In the axial part of the body: | ||
| 1. Muscles of the head and neck, | 75 | |
| 2. Muscles of the vertebral column and trunk, | 51 | |
| B. In the limbs: | ||
| 3. Muscles of the upper extremities, | 58 | |
| 4. Muscles of the lower extremities, | 59 | |
Flesh and blood have nearly the same ultimate composition. On evaporating 1000 parts of blood it yields 790 parts of water and 210 parts solid residue. The elements that enter into the composition of the solid matter are as follows:
| Flesh. | Blood. | |
| Carbon, | 51.86 | 51.96 |
| Hydrogen, | 7.58 | 7.25 |
| Nitrogen, | 15.03 | 15.07 |
| Oxygen, | 21.30 | 21.30 |
| Ashes, | 4.23 | 4.43 |
The general composition of a human muscle is shown by the following table: