20 



NATURE 



[May 3, 1888 



1. A posterior root, the ganglion of which is stationary in 

 position and is connected with both splanchnic and somatic 

 afferent nerves. 



2. An anterior root, the ganglion of which is vagrant, and is 

 connected with the efferent small- fibred splanchnic nerves. 



Also it is not a fundamental characteristic of a spinal nerve 

 that the anterior root should necessarily pass free from the 

 spinal ganglion, for it is clear that both anterior and posterior 

 roots may pass into the same stationary ganglionic mass if the 

 whole or part of the efferent ganglion has not travelled away 

 from the parent mass. This passage of the fibres of the anterior 

 as well as of the posterior roots into the spinal ganglion is com- 

 mon enough in the lower animals, and is a peculiarity of the 

 first two cervical nerves in such an animal as the dog. If, then, 

 the cranial nerves are formed on the same plan as the spinal, 

 their efferent roots ought to be divisible into a large-fibred non- 

 ganglionated portion and a small-fibred ganglionated portion, 

 the ganglia of which may be vagrant in character, while their 

 afferent roots should possess stationary ganglia near their exits 

 from the brain ; also the centres of origin for the different sets 

 of nerve fibres, i.e. for the splanchnic and somatic nerves, ought 

 to be the direct continuation of the corresponding centres of origin 

 in the spinal cord. Such I find to be the case ; if we leave out of 

 consideration the nerves of special sense, viz. the optic, olfactory, 

 and auditory nerves, the remaining cranial nerves are found to 

 divide themselves inio two groups — 



(1) A foremost group of nerves, which in man are entirely 

 efferent, viz. third, fourth, motor part of fifth, sixth, and seventh 

 nerves. 



(2) A hindmost group of nerves of mixed character, viz. ninth, 

 tenth, eleventh, and twelfth nerves, and the sensory part of fifth. 



The nerves of the first group resemble the spinal nerve s as far 

 as their anterior roots are concerned, for they are composed of 

 large-fibred non-ganglionated motor nerves and small-fibred 

 splanchnic efferent nerves, which possess vagrant ganglia, such 

 as the ganglion oculomotorii, the ganglion geniculaturo, &c. 



They resemble spinal nerves also as far as their posterior roots 

 are concerned, for they have formed upon them a ganglion at 

 their exit from the brain corresponding strictly to the stationary 

 posterior root ganglion of a spinal nerve. One great difference, 

 however, exists between their posterior roots and those of a 

 spinal nerve, for neither the nerve fibres nor the ganglion cells of 

 these roots are any longer functional ; they exist simply in the 

 roots of this group of cranial nerves in man, and other warm- 

 blooded animals, as the phylogenetically degenerated remnants 

 of what were in ages long since past doubtless functional ganglia 

 and functional nerve fibres. 



This foremost group of cranial nerves, then, is built up on 

 precisely the same plan as the spinal nerves ; the apparent 

 difference being due to the fact that the afferent roots with their 

 ganglia have degenerated. 



The hindmost group of cranial nerves is also composed of the 

 same constituents as the spinal nerves, and their different com- 

 ponents arise from centres of origin in the medulla oblongata 

 and in the cervical region of the spinal cord which are directly 

 continuous with the corresponding groups of nerve cells in other 

 parts of the spinal cord. Here, however, the deviation from 

 the spinal nerve type which has taken place consists not in the 

 suppression of any particular component, but in the scattering of 

 the various components, so that none of the nerves of this group 

 form in themselves complete segmental nerves, but rather the 

 whole of them taken together form a broken up group of 

 segmental nerves which are capable of being rearranged not 

 only into afferent and efferent but also into splanchnic and 

 somatic divisions of precisely the same character as in a group 

 of spinal nerves. 



I conclude therefore that both these two great groups of cranial 

 nerves are built up on the same plan as the spinal nerves, not 

 only with respect to the structure, function, and distribution of 

 their nerve fibres, but also as far as the arrangement of the 

 centres of origin of those nerve fibres in the central nervous 

 system is concerned ; and I think it probable that the reason for 

 the deviation of the cranial nerves from the spinal nerve type is 

 bound up with the changes which occurred at the time when a 

 large portion of the fibres of the foremost group of cranial 

 nerves lost their functional activity. I imagine that in the long 

 past history of the vertebrate animal some extensive tract in 

 connection with the foremost part of the nervous system has 

 become useless and disappeared, and in consequence the nerves 

 supplying those parts have degenerated. In this phylogenetic 



degeneration the whole of the splanchnic and somatic afferent 

 nerves of that region were involved, and probably also some of 

 the efferent nerve fibres, with the result that certain only of the 

 motor elements have remained functional. In the further history 

 of the vertebrate, the parts which have replaced those which 

 became useless have received their nerve supply from tracts of 

 the central nervous system situated behind this foremost group of 

 nerves ; in consequence of which the component parts of that 

 hindermost group have become more or less separated from each 

 other. The extent of the area involved is especially well seen 

 when the sensory nerves of this area, both somatic and splanchnic, 

 are considered ; for we see not only that the sensory part of the 

 trigeminal, representing the somatic sensory elements, and the 

 sensory part of the vagus, representing the splanchnic sensory 

 elements, are derived from their respective ascending roots, i.e. 

 arise in connection with a series of nerve segments extending 

 well into the cervical region, but also that the peripheral distri- 

 butions of these two nerves are very extensive. Without specu- 

 lating further at present upon the nature of the change which 

 has disturbed the orderly arrangement of the cranial nerves, 

 enough has been said to prove that the cranial nerves considered 

 in this article are built up on the same plan as the spinal nerves. 

 Further it is worthy of notice that just as the division into 

 somatic and splanchnic has thrown great light upon the concep- 

 tion of the manner in which a segmental nerve is formed, so also 

 it lends aid to the consideration of the segmentation of structures 

 other than the nervous, for we find that two distinct segmentations 

 exist in the body which do not necessarily run parallel to each 

 other : the one, a segmentation which may be fitly called splanch- 

 nic, and is represented by the orderly arrangement of visceral 

 and branchial clefts ; and the other, a somatic segmentation, 

 characterized by the formation of somites, i.e. of vertebrae and 

 somatic muscles arranged also in orderly sequence. 



The splanchnic segmentation is most conspicuous in the cranial 

 region, the somatic segmentation in the spinal region, and it is 

 most advisable to remember that a valid comparison between 

 cranial *and spinal segments can only be made when like is com- 

 pared with like, for it by no means follows that the somatic and 

 splanchnic segmentations have proceeded on identical lines ; 

 consequently, in comparing cranial with spinal nerves, we must 

 compare structures of the same kind, and seeing that the spinal 

 nerves are arranged according to somatic segments so also must 

 the cranial nerves be arranged in accordance with their relation 

 to the somatic muscles of the head, and not in relation to the 

 branchial and visceral clefts. 



It is not advisable in this article to enter upon any discussion 

 as to the number of segments supplied by the cranial nerves, or 

 to speculate upon the nature of the changes which have taken 

 place in the past history of the vertebrate animal, whereby the 

 present distribution of the cranial nerves has been brought about. 

 I desire only to put as shortly as possible before the readers of 

 Nature the general results of my recent investigations into the 

 structure of the cranial and spinal nerves. 



W. H. Gaskeix. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Cambridge. — Mr. T. C. Fitzpatrick, of Christ's College, has 

 been appointed an Assistant Demonstrator of Physics. 



Prof. H. M. Ward, M.A., of Christ's College, has been 

 appointed Examiner in Botany in the place of Prof. Bayley 

 Balfour. 



Dr. R. D. Roberts has been appointed an Elector to the 

 Harkness Scholarship. 



The name of Mr. Adami, the new Demonstrator of Pathology, 

 was misprinted Adams in our last issue. 



SCIENTIFIC SERIALS. 



Bulletin de I'Academie Royale de Belgique, February. — 

 Researches on the coll >idal state, by C. Winssinger. This is 

 the first part of a memoir describing a series of experiments 

 undertaken to determine the various conditions of the colloidal 

 state — that is, of the state assumed under certain circumstances 

 by bodies generally insoluble in water. For the present the 

 author confines himself to describing the mode of preparation 

 1 and the chief properties of the colloidal substances. All the 



