OLFACTOKY NEKVES. 



767 



cerebro -spinal nervous system, it is certain that the cells and fibres of the sympathetic system 

 possess a vital activity apart from their connexion with the central nervous system. In the 

 development of the sympathetic it is at least highly probable that a mesoblastic rudiment or 

 precursor forms the basis of the sympathetic system, which is secondarily joined by nerve- 

 fibres from the roots of the spinal nerves. 



Morphologically this part of the nervous system is essentially a longitudinal cord or column, 

 associated with involuntary muscles and glandular tissues, and particularly related to the organs 

 in the splanchnic area. Like other longitudinal structures in the body, and especially like the 

 organs of the splanchnic area, the sympathetic system is not truly segmental. The sympathetic 

 trunk is only quasi-segmental, the segmentation being attributable to its junction with the 

 visceral branches of the spinal nerves. The peripheral branches from the sympathetic trunk are 

 by no means segmental ; even the gray rami are not properly metameric, but, like the ganglia, 

 assume a segmental character in consequence of their connexions with the spinal nerves. 



The phylogenetic relation of the sympathetic and the cerebro-spinal elements in the system 

 it is impossible to determine. It may be that the sympathetic system is the representative of 

 an ancient architecture independent of the cerebro-spinal nervous system, the materials of which 

 are utilised for a more modern nervous system ; or it may be that the correlation of spinal 

 nerves and sympathetic are both the consequences of the formation of new organs and structures 

 in the splanchnic area. Examined in every light, it possesses features which effectually differ- 

 entiate it from the cerebro-spinal system, although it has become inextricably united with it 

 and subservient to it. 



THE CEEEBEAL NERVES. 



See note, p. 798. 



'he deep connexions of the cerebral nerves are dealt with in the section 

 ( which treats of the Brain (pp. 592 to 607). Certain general points in connexion 

 with these nerves are also touched upon in the chapter introductory to the 

 Nervous System (p. 500). Their development is given on p. 501 et seq. 



NERVI OLFACTORII. 



In the older accounts, the first or olfactory nerve is described as consisting 

 of several parts : (1) a series of fine nerves, which arise from (2) the olfactory 

 bulb. This again is connected by (3) the olfactory tract with the brain, to which 

 lit is attached by (4) two striae or roots (Fig. 643). 



The anatomy of the olfactory bulb, the olfactory tract and its roots is described 

 elsewhere (pp. 623 to 628). 



The olfactory nerve consists of about twenty separate filaments which arise in 



