and arranged, that a point, destitute of a nerve, cannot be found on the skin.
Some idea of the ramifications of the nerves, may be obtained by reference to the following engraving, (Fig. 8.) In this, A, A, represents the cerebrum, or great brain; B, B, the cerebellum, or little brain; (see also a, b, in Fig. 6;) C, C, represents the union of the fibres of the cerebrum; D, D, the union of the two sides of the cerebellum; E, E, E, the spinal marrow, which passes through the centre of the spine, (as seen at c, d, e, in Fig. 6;) 1, 2, 3, 4, 5, 6, branches of the nerves going to different parts of the body. As the nerves are the organs of sensation, all pain is an affection of some portion of the nerves. The health of the nerves depends very greatly on the exercise of the muscles, with which they are so intimately connected. This shows the reason why the headache, tic douloureux, diseases of the spine, and other nervous affections, are so common among American women. Their inactive habits, engender a debility of the nervous system, and these diseases follow, as the consequence.
Fig. 8.
It can be seen, by a reference to the side view, represented on page 77, (Fig. 6,) that the spine is naturally curved back and forward. When, from want of exercise, its bones are softened, and the muscles weakened, the spine acquires an improper curve, and the person becomes what is called crooked, having the neck projected forward, and, in some cases, having the back convex, where it should be concave. Probably one half of the American women have the head thus projecting forward, instead of carrying it in the natural, erect position, which is both graceful and dignified.
The curvature of the spine, spoken of in this work as so common, and as the cause of so many diseases among American women, is what is denominated the lateral curvature, and is much more dangerous than the other distortion. The indications of this evil, are, the projection of one shoulder blade more than the other, and, in bad cases, one shoulder being higher, and the hip on the opposite side more projecting, than the other. In this case, the spine, when viewed from behind, instead of running in a straight line, (as in Fig. 7 and 9,) is curved somewhat, as may be seen in Figures 10 and 11.
This effect is occasioned by the softness of the bones, induced by want of exercise, together with tight dressing, which tends to weaken the muscles that are thus thrown out of use. Improper and long continued positions in drawing, writing, and sleeping, which throw the weight of the body on one part of the spine, induce the same evil. This distortion is usually accompanied with some consequent disease of the nervous system, or some disarrangement of the internal organs.
By comparing Figures 9 and 11, the difference between a natural and distorted spine will be readily perceived. In Fig. 10, the curved line shows the course of the spine, occasioned by distortion; the perpendicular line, in this and Fig. 11, indicates the true direction of the spine; the horizontal lines show that one shoulder and hip are forced from their proper level.
Fig. 9.
Fig. 10.
Fig. 11.
BLOOD-VESSELS
The blood is the fluid into which our food is changed, and which is employed to minister nourishment to the whole body. For this purpose, it is carried to every part of the body, by the arteries; and, after it has given out its nourishment, returns to the heart, through the veins.
The subjoined engraving, (Fig. 12,) which presents a rude outline of the vascular system, will more clearly illustrate this operation, as we shall presently show.
Fig. 12.
Before entering the heart, the blood receives a fresh supply of nourishment, by a duct which leads from the stomach. The arteries have their origin from the heart, in a great trunk, called the aorta, which is the parent of all the arteries, as the spinal marrow is the parent of the nerves which it sends out. When the arteries have branched out into myriads of minute vessels, the blood which is in them passes into as minute veins; and these run into each other, like the rills and branches of a river, until they are all united in two great veins, which run into the heart. One of these large receivers, called the vena cava superior, or upper vena cava, brings back the blood from the arms and head, the other, the vena cava inferior, or lower vena cava, brings back the blood from the body and lower limbs.
In the preceding figure, H, is the heart, which is divided into four compartments; two, called auricles, used for receiving the blood, and two, called ventricles, used for sending out the blood. A, is the aorta, or great artery, which sends its branches to every part of the body. In the upper part, at a, a, a, are the main branches of the aorta, which go to the head and arms. Below, at a, a, are the branches which go to the lower limbs. The branches which set off at X, X, are those by which the intestines are supplied by vessels from the aorta. Every muscle in the whole body, all the organs of the body, and the skin, are supplied by branches sent off from this great artery. When the blood is thus dispersed through any organ, in minute vessels, it is received, at their terminations, by numerous minute veins, which gradually unite, forming larger branches, till they all meet in either the upper or lower vena cava, which returns the blood to the heart. V I, is the vena cava inferior, which receives the blood from the veins of the lower parts of the body, as seen at v, v. The blood, sent into the lower limbs from the aorta, is received by minute veins, which finally unite at v, v, and thus it is emptied through the lower vena cava into the heart: o, o, represent the points of entrance of those tributaries of the vena cava, which receive that blood from the intestines, which is sent out by the aorta at X, X. In the upper part, V S, is the vena cava superior, which receives the blood from the head and arms; v, v, v, are the tributaries of the upper vena cava, which bring the blood back from the head and arms; d, d, represents the course of the thoracic duct, a delicate tube by which the chyle is carried into the blood, as mentioned on page 89; t, shows the place where this duct empties into a branch of the vena cava.
It thus appears, that wherever a branch of the aorta goes to carry blood, there will be found a tributary of the upper or lower vena cava, to bring it back.
The succeeding engravings, will enable the reader to form a more definite idea of this important function of the system,—the circulation of the blood. The heart, in man, and in all warm-blooded animals, is double, having two auricles and two ventricles. In animals with cold blood, (as fishes,) the heart is single, having but one auricle and one ventricle. Fig. 13, represents the double heart as it appears when the two sides are separated, and also the great blood-vessels; those on the left of the figure being on the right side of the body, and vice versa. The direction of the blood is represented by the arrows. A, represents the lower vena cava, returning the blood from the lower parts of the body, and L, the upper vena cava, returning the blood from the head and arms. B, is the right sinus, or auricle, into which the returned blood is poured. From this
