CHAPTER II. 



THE NERVOUS SYSTEM. 



WE have examined into the basal nature of the substance composing 

 animal bodies so far as it may readily be studied, and have noted its 



FIG. 20 

 MESENCEPHALON 



FIG. 21 



CHOROID 



PLEXUS 



FORAMEN 



OF MONRO 



CAUDATE 



NUCLEUS 



INFUNDIBULUM PONS 



CEREBELLUM 



FOURTH 



VENTRICLE 



OBLONGATA 



Brain of calf-embryo of 5 cm., to show the ben dings of 

 the originally straight neural axis. Lateral view of left 

 side, the outer wall of the hemisphere being removed. 

 (Hertwig.) 



activities. We can now discuss the func- 

 tions of the human body systematically 

 and with as mueh detail as our space al- 

 lows. In this description of bodily pro- 

 cesses we must first understand the ways 

 by which the various parts and functions 

 of the body are coordinated so as to 

 constitute an individual. Animals exist 

 only as individuals, and in part at least, 

 as the name implies, are separate from 

 each other and more or less independent. 

 Without a proper understanding of the 



means of unification of the various functions we should miss the full 

 meaning of many of them and fail utterly to take that broad view of 

 animal life which is so essential to knowledge and invaluable in treating 

 diseased conditions. We should never think of the animal, then, as a 

 group of organs but as one integral organism, though necessarily made 

 up of parts more or less different in their structure and uses. It is ex- 

 ceedingly important to keep in mind this inherent unification and to 

 remember that it is for descriptive purposes only that we should separate 

 the organs and describe them one at a time. In reality, as they live, 

 they are in no sense independent of each other. One of the means 



Very early state of the central ner- 

 vous system of man : 1, 2, 3, forebrain, 

 midbrain, and hindbrain, respectively; 

 7, telencephalon; Op. v., optic vesicle; 

 II, diencephalon; ///, mesencephalon; 

 /T.metencephalon; F.myelencephalon. 

 Farther down the neural groove one 

 sees the somites and medullary groove 

 of the spinal cord. (Hackel.) 



