COXXECTION OF NERYE-FIBRES WITH CELLS. 143 



branches of nerves still requires further investigation. For some interesting 

 observations on the subject the reader is referred to a paper by Beale.* 



Origins or Roots of the Nerves. — The cerebro-spiual nerves, as 

 alread}' said, are connected b}^ one extremity to the brain or to the 

 spinal cord, and this central extremity of a nerve is, in the language of 

 anatomy, named its origin or root. In some cases the root is single, 

 that is, the funiculi or fibres by which the nerve arises are all attached 

 at one spot or along one line or tract ; in other nei'ves, on the contrary, 

 they form two or more separate collections, which arise apart from each 

 other and are connected with different parts of the nervous centre, and 

 such nerves are accordingly said to have two or more origins or roots. 

 In the latter case, moreover, the different roots of a nerve may differ 

 not only in their anatomical characters and connections, but also in 

 function, as is well exemplified in the spinal nerves, each of which 

 arises by two roots, an anterior and a posterior — the former containing 

 the raotor fibres of the nerve, the latter the sensory. 



The fibres of a nerve, or at least a considerable share of them, may 

 be traced to some depth iu the substance of the brain or spinal cord, 

 and hence the term " apparent or superficial origin" has been employed 

 to denote the place where the root of a nerve is attached to the surface, 

 in order to distinguish it from the " real or deep origin " which is 

 beneath the surface and concealed from view. 



To trace the different nerves back to their real origin, and to determine the 

 points where, and the modes in which their fibres are connected with the nervous 

 centre, is a matter of great difficulty and uncertainty ; and, accordingly, the 

 statements of anatomists respecting the origin of particular nerves are in many 

 cases conflicting and unsatisfactory. Confining ourselves here to what applies 

 to the nerves generally, it may be stated, that their roots, or part of their roots, 

 can usually be followed for some way beneath the surface, in form of white 

 tracts or bands distingiiishable from the sturounding substance ; and very gene- 

 rally these tracts of origin may be traced towards dei^osits of grey nervous matter 

 situated in the neighliourhood ; such, for instance, as the central grey matter of 

 the spmal cord, the grey centres of the pneumo-gastric and glosso-pharyngeal 

 nerves, the corpora geniculata and other larger grey masses connected with the 

 origin of the optic nerve. It would further seem probable that certain fibres of 

 the nerve-roots take their origin in these local deposits of gi'ey matter, whilst 

 others become continuous with tlie white fibres of the spinal cord or encephalon, 

 which are themselves connected with tlie larger and more general collections 

 of grey matter situated in the interior or on the surface of the cerebro-spinal 

 •centre. 



There is still much uncertainty as to the precise mode in which the 

 nerve-fibres originatiug or terminating in the grey matter are related to 

 its elements, and for the most part, indeed, individual fibres on being- 

 traced into the grey matter, become so hidden in the mass as to elude 

 farther scrutiny. JSTevertheless, as a continuity between the nerve-fibres 

 and nerve-cells in the grey matter has now been traced in individual 

 examples by many different observers, and as such connections may be 

 held to be general in the ganglions, it is not unfair to infer that, but for 

 the obstacles to successful investigation, the cells in the grey matter of 

 the cerebro-spinal centre would by this time also have been shown to 

 be generally connected with the nerve-fibres. 



* On the Branching of Nerve-Trunks, &c., Archives of Medicine, vol. iv., p. 127. 



