270 



FIFTH PAIR OF NERVES. 



very probable, inasmuch as Cloquet takes no 

 account of fasciculi, and in his description of 

 the smaller packet it is manifest that he has 

 assumed the fasciculi, of which it is composed, 

 to be filaments, for he does not attribute to it 

 a greater number of filaments than it contains 

 of fasciculi. But if Cloquet have underrated 

 the filaments of the larger packet, Meckel 

 junior has certainly overrated the fasciculi of 

 the smaller one. From his account of the 

 latter, it is to be concluded that it contains 

 from three to fourteen fasciculi, but either of 

 those numbers is too great, as will be seen 

 from an examination of the subject, from which 

 it will appear that they do not exceed the 

 number attributed to them by Cloquet. The 

 ultimate number of filaments, however, would 

 seem to be somewhat uncertain, for it appears 

 to depend very much upon the delicacy with 

 which the separation of them may be effected ; 

 and after all it is not a matter of any great 

 importance. According to Wrisberg* and 

 Scemmerring-f the number of fibres contained in 

 the greater packet is always less in the foetus 

 than in the adult. The filaments of the smaller 

 are stated by Cloquet to be larger, softer, and 

 whiter than those of the other; but with regard 

 to the difference of size it is probable that 

 this opinion has arisen also from his having 

 assumed the fasciculi to be filaments, inas- 

 much as, when the fasciculi have been decom- 

 posed, the filaments seem to be equally fine in 

 both packets ; and for the other points of sup- 

 posed difference the author has not been able 

 satisfactorily to observe any in man. In other 

 animals, however, in some fish at least a 

 remarkable difference may be observed between 

 the characters of the ganglionic and non-gan- 

 glionic portions, the latter of which, in the 

 Cod, is much softer, and of a darker, not 

 whiter, colour than the other. 



The fascicular and filamentous disposition 

 which has been described, is not, however, 

 presented by the encephalic portion of the 

 nerve through its entire extent, but only in 

 that part of it which is superficial to the brain ; 

 nor is it acquired by it until after it has emerged 

 one or two lines from the substance of the 

 organ, and then it does not assume it through- 

 out at once, but at first superficially and later 

 internally. The appearance of distinct fila- 

 ments and fasciculi in one part and their ab- 

 sence in the other appears owing to the exist- 

 ence of neurilema in the former, for in one 

 as in the other the nervous matter appears to 

 be arranged in longitudinal tracts, which pre- 

 sent in one case the form of expansions, and 

 in the other are divided by the neurilema 

 into separate cords ; and again the occurrence 

 of the filamentous disposition earlier upon the 

 surface than internally, is attributed to the 

 superficial substance of the nerve being pro- 

 vided with neurilema sooner than the inter- 

 nal ; hence the length of the substance of the 

 nerve without neurilema is greater internally 



* Observations Anatomies de quinto pari ner- 

 vorum, &c. 



t In Lmdvvig, Script, Ncurol. Min. Ueber das 

 Organ der Seele. 



than externally, and when the nerve has been 

 pulled away from its attachment to the brain, 

 the rupture occurring at the point at which the 

 neurilema commences, the part which is left 

 projects in the middle, and presents a conical 

 eminence of white matter: this, as Cloquet 

 justly remarks, is but an incidental appearance, 

 and not entitled to be considered, as it was by 

 Bichat,* a real tubercle, from which the nerve 

 arose. In neither packet are the fasciculi 

 laid simply in apposition ; in both, but more 

 remarkably in the larger, they are connected 

 by frequent interchanges of filaments, and 

 that to such a degree that the nerve when 

 opened out appears to form an inextricable 

 plexus, in which it is not improbable that every 

 filament of it is connected directly or indirectly 

 with all the others; this plexiform arrangement 

 diminishes as the nerve approaches the gan- 

 glion, before reaching which the fasciculi be- 

 come more distinct. 



The fifth nerve is attached to the surface of 

 the brain on either side of the pons Varolii, at 

 a distance of three-fourths of an inch from its 

 middle line. It is attached to the middle 

 cms of the cerebellum, on its anterior inferior 

 surface, about one-fourth of an inch from its 

 superior, and half an inch from its inferior 

 margin. 



The place of the attachment of the nerve to 

 the exterior of the brain varies greatly in dif- 

 ferent classes of animals ; in man, it is, as has 

 been mentioned, the crus cerebelli on either 

 side of the pons; in the other orders of the 

 Mammalia it is either, as in the human sub- 

 ject, the crus cerebelli, or, when the pons is 

 less developed than in man, the nerve is at- 

 tached behind that part between it and the 

 trapezium of the medulla oblongata; in the 

 other three classes of vertebrate animals, in 

 which the pons and trapezium are both want- 

 ing, the nerve is uniformly attached to the la- 

 teral parts of the spinal bulb. This contrast 

 is equally curious and important ; it affords us 

 a natural analysis, which will throw much light 

 on the next step in our inquiry, viz. the origin 

 of the nerve, or its ultimate connexion with 

 the brain. It furnishes also, as has been sug- 

 gested by Gall and Spurzheim,f an explana- 

 tion of the complication which exists in the 

 human being, in whom the great developement 

 and the situation of the pons render it neces- 

 sary that the nerve should traverse it, in order 

 to reach the surface of the brain. 



At the attachment of the nerve to the crus 

 cerebelli in the human subject, the non-gan- 

 glionic portion or lesser packet is situate above 

 and to the inner side of the greater. At that 

 place it is separated or separable into two 

 parts, while the greater continues undivided, 

 and hence the nerve is described as having 

 three roots, one for the greater and two for 

 the lesser packet. The existence of two roots 

 for the lesser packet had been announced by 

 Santorini^J but they have been more parti- 



* Anatomie Descriptive. 



t Anatomie et Physiologic du Systeme Nerveux. 



J Observationes Anatomicae. 



