ROOTS OF NERVES. cxlvii 



of nerves still requires further investigation. For some interesting observations on 

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



Origins or Roots of the Nerves. The cerebro- spinal nerves, as already 

 said, are connected by 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 fuiiiculi or 

 fibres by which the nerve arises are all attached at one spot or along one 

 line or tract ; in other nerves, 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 origin* 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 motory 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 in 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 dis- 

 tinguish 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 our- 

 selves 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 be- 

 neath the surface, in form of white tracts or bands distinguishable from the 

 surrounding substance ; and very generally these tracts of origin may be 

 traced towards deposits of grey nervous matter situated in the neighbour- 

 hood ; such, for instance, as the central grey matter of the spinal cord, the 

 grey centres of the pueiuno-gastric and glo.-so-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 grey matter, whilst others 

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

 which are themselves connected with the 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 originating or terminating in the grey matter are related to its ele- 

 ments, and for the most parb, indeed, individual tibres on being traced into 

 the grey matter, become so hidden in the mass as to elude further scrutiny. 

 Nevertheless, 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. 



