The Creation of God, Jacob Hartmann [e manga reader TXT] 📗
- Author: Jacob Hartmann
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Muscular fibers consist each of a tube or sheath of delicate structureless membrane, inclosing a number of filaments or fibrils. They are of cylindrical form, or of prismatic with one or more sides, according to the manner in which they are compressed by adjacent tissues. Their average diameter is about 1⁄500 of an inch, and their length never exceeds an inch and a half.
The arrangement of the elementary substances in a muscular fiber (the sarcos element or protoplasm inclosed in the sarcolemna, the sheath) composing a muscular fiber may be compared to Volta’s pile or an electric battery. In fact, both muscle and nerve are made up of electrical molecules, each of the two ends of which is negative—though the development of the electrical current is at present very imperfectly known.
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):
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:
The general composition of a human muscle is shown by the following table:
The muscles of the flesh form a large proportion of the weight of the whole body. Calculated for a man of 150 pounds’ weight:
The property of muscular tissue by which its peculiar functions are exercised, is its contractility—contraction or shortening. This is excited by all kinds of stimuli, applied either directly to the muscles, or indirectly to them through the medium of their nerves.
The muscular tissues perform all the physical work—as locomotion, every kind of action and exertion—of the body.
The quantity of blood circulated through the body is estimated to be from about 1⁄10 to about 1⁄13 part of the body’s weight, and about ¼ of that is distributed in the muscles.
As regards the action of the muscles the following general principles ought to be kept in view:
1. That the force exerted by any muscle during its contraction is in proportion to the number of muscular elements or fibers composing the muscle.
2. That the extent of motion, in so far as it merely depends on the shortening of the fibers of the muscle, is in proportion to the length of the fibers.
3. That the direction of the force produced by a contracting muscle is in the line of the axis of the whole muscle if it runs straight between its opposite points of attachment, but in the line of the portion attached to the moving part of the muscle, or its tendon, if it be bent in its course, etc.
The Nervous Tissue.
The nervous system consists of the cerebrum, pons varolii, cerebellum, medulla oblongata, the spinal cord with its nerves and the sympathetic ganglia, etc.
The cerebrum or brain proper constitutes the highest and much the largest portion of the encephalon. The cerebrum consists of two halves, that are connected with each other by the corpus callosum, and with the peduncular masses of the cruri cerebri, the processus a cerebello ad cerebrum; the series of eminences, or cerebral centers or ganglia, concealed from view, named corpora quadrigemina, optic thalamus and corpora striata, etc.
The cerebral hemispheres are by far the most bulky part of the cerebrum. Various commissural structures unite the two hemispheres, including the corpus callosum and fornix; and some smaller structures, viz., the pineal gland, the petuitary bodies, and the olfactory bulb.
The cerebral hemispheres together form an ovoid mass, in contact with the vault of the cranium, and with its smaller end forward, its greatest width being opposite to the parietal eminences. They are separated in the greater part of their extent by the great longitudinal fissure.
The surface of the hemisphere is composed of gray matter, and is molded into numerous smooth tortuous eminences, named convolutions, or gyri, which are marked off from one another by deep furrows, called sulci.
The cerebrum is divided into lobes for convenience of study, five in number, called frontal, parietal, occipital, temporal, sphenoidal, and central.
The internal structure of the cerebrum is composed of white matter. It consists of tubular fibers varying in size in various parts, but in general still smaller than those in the cord, their average diameter being 1⁄10000 of an inch. The fibers of white substance present no division. They are arranged in bundles, separated by a network of delicate connective tissue, consisting of cells, etc. The cells are of various forms and sizes—spheroidal, angular, fusiform, etc. The fibers radiate from the white center of each convolution in all directions into the gray cortex, having a course for the most part perpendicular to the free surface. In passing through the gray substance they are arranged in bundles about 1⁄1500 of an inch in diameter, thus separating some of the nerve cells, etc.
The olfactory tract and bulb, the corpora quadrigemina, corpora genicolate, optic thalamus, corpora striata, are all more or less mixed. They possess gray matter.
The nerves immediately connected with the brain are of several kinds. And there are twelve pairs of them. They are called cerebral nerves.
There are four kinds.
1. Nerves of special sense.
2. Nerves of common sensation.
3. Nerves of motion.
4. Mixed nerves of sensation and motion.
The nerves of special sense may with great propriety be termed the nerves of observation, perception—the gateways of intelligence and education.
I.—Nerves of special sense:
1. The olfactory supplies the nose, special sense of smell.
2. The optic supplies the eye, special sense of sight.
3. The auditory supplies the ear, special sense of hearing.
4. Part of the glosso-pharyngeal supplies the tongue and pharynx.
5. The gustatory, lingual branch of the fifth, supplies the tongue, sense of taste.
II.—Nerves of common sensation:
1. The ophthalmic supplies the eye.
2. The superior maxillary supplies the upper jaw and teeth.
3. The inferior maxillary supplies the lower jaw and teeth.
III.—Nerves of motion:
5. The facial nerve supplies the muscles of the face.
6. The hyperglossal supplies the muscles of the tongue.
IV.—Mixed nerves:
1. The pneumogastric supplies lungs, heart, stomach, larynx, etc.
2. The spinal accessory supplies some muscles of the back.
The average weight of the brain in the adult male is about 49½ ounces, a little more than three pounds avoirdupois; in the female 44 ounces; the average difference between the two being from 5 to 6 ounces.
The spinal cord has a length of about 16 to 17 inches, and weighs about 1½ ounces.
The spinal cord is a continuation of the medulla oblongata, is lodged in the spinal canal, and gives off 31 pairs of nerves, that supply all the muscles of the body with sensitive and motor nerves.
The medulla oblongata is pyramidal in form, having its broad extremity upwards. It is expanded laterally at its upper part. Its length from the pons varolii to the lower extremity of the pyramid is about an inch and a quarter; its greatest breadth is nearly an inch; and its thickness from before backwards is about three-quarters of an inch.
The medulla is the link between the brain and the spinal cord. The majority of centers for various organic functions are situated in it; as follows:
1. The respiratory center, with its neighboring convulsive center (venous blood excites convulsive centers, etc.). 2. The vaso-motor center. 3. The cardiac-inhibitory center. 4. The diabetic center, or center for producing artificial diabetes. 5. The center for deglutition. 6. The center for the movements of the æsophagus, with its vomiting center. 7. The center for reflex excitation of the secretion of saliva, with which may be associated the center through which the væjus (pneumogastric) influences the secretions of pancreatic juice, and possibly of the other digestive juices. 8. The center for the dilation of the pupil by means of the cervical sympathetic.
From the surface of the medulla certain of the cranial nerves arise, namely the sixth (abducens), glosso-pharyngeal, pneumogastric, spinal accessory, etc.
The fibers from the spinal cord pass upwards through the medulla oblongata and various other structures and finally reach the cerebrum.
The cerebellum, or hinder brain, consists of a body, and of three pairs of crura or peduncles, by which it is connected with the rest of the cerebro-spinal axis. The cerebellum is covered with a gray cortical substance, rather darker than that of the cerebrum. Its greatest diameter is transverse, and extends to about three and a half or four inches; its width from before backwards is about two or two and a half inches; and its greatest depth is about two inches, but it is much thinner round its outer border. It consists of two lateral hemispheres joined by a median portion called the vermiform process, and other structures therewith connected, etc.
Minute structure: The cortical gray substance is composed of an external clear gray layer, an inner grayish-red “granule” layer, and between the two a single layer of large cells with long processes, termed the corpuscles of Porkinge (after the man who first described them). Outside all is the layer of fibers and vessels of the pia mater. The external layer consists of a delicate matrix, probably of the nature of connective tissue, consisting of cells and fibers, etc.
The cerebellum is probably concerned in the coördination of movements. Its functions seem
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