CHAPTER V 



THE GENERAL ANATOMY OF THE NERVOUS 



SYSTEM 



IT has been possible to proceed to this point with only 

 the most general statement of the spatial arrangement of 

 the parts which are united to form the nervous system. 

 A certain amount of detail must now be supplied. It will 

 be helpful to make some comparisons between what is to 

 be seen in the simpler vertebrates and what is found in 

 man. No description of the invertebrate organi/.atioii 

 will be undertaken; it is most interesting but peculiarly 

 difficult to bring into line with the higher lype. 



Let us attend to the outlines of the nervous mechanism 

 as exemplified in the frog, an animal which has been chosen 

 for very many of the cardinal researches upon this system. 

 Here, as always, we recognize an axial or central portion 

 and the nerves extending from it to all parts of the body. 

 The axial portion is said to consist of the brain and the 

 spinal cord. The brain is lodged in the cavity of the skull; 

 the cord extends through a canal made by the successive 

 arches of the vertebra-, the individual bones of the spinal 

 column. Those nerves which take their rise from the 

 brain are called cranial, the reference being to the cranium, 

 which is the portion of the skull bounding the brain. 

 The nerves originating from the cord are called x/n'nal. 

 The cranial nerves issue from the skull through openings 

 which are called foramina. The spinal nerves find their 

 way through notches between adjacent vertebra', inter- 

 vertebral foramina, &B they are called. The number of 

 both the cranial and the spinal nerves is smaller in the 

 frog than in many of the higher forms, including man. 

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