80 THE STRUCTURE OF 



Without entering upon any discussion as to the differ* 

 ences existing between the nerve elements of higher and of 

 lower animals, and dwelling but briefly upon the many 

 differences of opinion which exist in regard to the actual 

 structure and relations of these elements, an endeavour 

 will be made to give the reader some notions concerning 

 their most probable arrangement — such notions as 

 may enable him to comprehend the descriptions given in 

 succeeding chapters of the different forms of the nervous 

 system, as well as of the nature and mode of composition 

 of that portion of it known as the ' brain', in various orders 

 of animals till we come to man himself. In this way 

 it will be possible for the reader who bestows an adequate 

 amount of attention, to obtain a good insight as to the 

 nature of some of the most definite and best-grounded 

 notions, which are at present either actually held or 

 warrantable, concerning the structure and functions of 

 the * Brain as an Organ of Mind.' 



Nerve Fibres. — At their commencement near the 

 internal and external surfaces of the body, and also near 

 their endings in muscles and glands, nerves are repre- 

 sented by extremely fine, almost transparent ' fibrils ' from 



"6 00^^ to ■nnuT'oTT^^^ ^^ ^^ ^^^^ ^^ diameter. These 

 fibrils freely interlace with one another, so as to form 

 minute loops and plexuses, and, within short distances, 

 they often vary considerably in diameter (L. Beale). 



Much might be written were we to attempt to discuss 

 the various modes in which the fibrils commence or termi- 

 nate, and their precise relation to other tissue elements in 

 various parts of the body ; but, in spite of the great 

 interest attaching to these questions, they cannot be 

 entered upon in this work. A slight reference to the 

 Bubject is, however, made (p. 67) in the next chapter. 



