CHAPTER II. 



THE NERVOUS SYSTEM IN GENERAL. 



SECTION I. WHAT PARTS IT INCLUDES. 



The nervous system, as well in man as in the animals in 

 any way d:'elated to him, comprises the cerebrum, cerebellum, 

 medulla oblongata, medulla spinalis, and all the nerves dis- 

 tributed thence to every part of the body. These divisions are 

 manifestly dissimilar in structure; those portions whose functions 

 are more numerous and complicated seem to require a more 

 composite and complicated structure than those whose functions 

 in the animal economy are of a simpler kind ; in particular, 

 the brain of man is larger and of a more complex structure 

 than the cerebellum, and other portions of the nervous system. 

 This large cerebrum is divided into two hemispheres, united 

 in the middle principally by the corpus callosum : the gray cor- 

 tical matter entirely surrounds the white internal medullary 

 matter, which is in much greater quantity in the cerebrum than 

 in the cerebellum : the external surface appears as if divided 

 into convolutions, having a resemblance to the intestines. The 

 cerebrum has three cavities, or ventricles, in the two superior 

 of which are seen the plexus choroides, then the corpora striata 

 and thalami nervorum opticorum ; behind these, are the pineal 

 gland and corpora quadrigemina. The septum lucidum divides 

 these ventricles, beneath which is the fornix divided posteriorly 

 into two crura, termed pedes hippocampi and cornua am- 

 monis. In the third ventricle, are the anterior and posterior 

 commissures; also, posteriorly, the opening into the fourth 

 ventricle, which is in the cerebellum, and, anteriorly, the orifice 

 into the infundibulum, which is inserted into the pineal gland. 

 Posteriorly to the infundibulum, are seen the corpora mamil- 

 laria, and here are also situate the two great crura cerebri into 

 which all the medullary matter from both hemispheres seems 

 to be collected. The cerebellum is much less than the cere- 

 brum, and presents on its surface highly-curved and slender 

 convolutions; its medullary matter is much less in proportion to 



