. Animal physiology. Physiology, Comparative; Physiology, Comparative. 56 NERVOUS SYSTEM, AND GENERAL STRUCTURE, OF VERTEBRATA. vertebral column ; and of nervous trunks proceeding from these, which are distributed to all parts of the body. The brain and spinal cord are termed the nervous centres ; since it is in them that the power of this system resides; the trunks or cords being only conductors of its influ- ence. The distinguishing feature of this system in Yertebrata is, that its several centres are thus united into one large mass, instead of forming a number of separate small masses or ga
. Animal physiology. Physiology, Comparative; Physiology, Comparative. 56 NERVOUS SYSTEM, AND GENERAL STRUCTURE, OF VERTEBRATA. vertebral column ; and of nervous trunks proceeding from these, which are distributed to all parts of the body. The brain and spinal cord are termed the nervous centres ; since it is in them that the power of this system resides; the trunks or cords being only conductors of its influ- ence. The distinguishing feature of this system in Yertebrata is, that its several centres are thus united into one large mass, instead of forming a number of separate small masses or ganglia, as we shall find that they do in the lower classes of ani- mals : and that it is enclosed in the bony casing, which has been described as pecu- liarly destined for its protection, instead of being enveloped with all the other organs, in a hard covering, as in the lobster ; or of being entirely destitute of protection, as in the slug. That it should receive this pecu- liar protection is quite necessary, in conse- quence of the much higher development which it attains, and the much greater importance which it possesses, in this divi- sion of the animal kingdom, than in any other. 66. The general arrangement of the other organs in Vertebrated animals, is shown in the succeeding page (Fig. 8). At m is seen the mouth, forming the entrance to the digestive cavity, of which the termination is at the oppo- site extremity of the body; i, i, is the intestinal canal, and 7, the liver : these organs occupy the part of the body which is called the abdomen or belly. The mouth also opens, however, into the windpipe or trachea, t, which conducts air into the lungs, p; these organs, with the heart, h, are contained in the portion of the trunk called the thorax, or chest. At b is seen the position of the brain ; and at 5 that of the spinal Fig. 7.—Brain and Spinal Cord of Please note that these images are extracted from scanned page images that may have been digitally enhan
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