FIFTH PAIR OF NERVES. 



273 



the same part as the greater packet, and poste- 

 rior to it. (See jig. 140). This view of the con- 

 nection of the lesser packet, if confirmed, must 

 lead to interesting results with regard to the rela- 

 tions of the two portions of the fifth nerve at least; 

 it will at all events decide the question as yet in 

 dispute, whether they are to be regarded as 

 distinct nerves, or parts of the same ; upon 

 this point further light will be thrown by the 

 disposition of the same part in fish, in which 

 the source of the uncertainty prevailing with 

 regard to the nerve in the higher classes does 

 not exist to the same amount ; inasmuch as the 

 ganglionic and non-ganglionic divisions of the 

 nerve seem for the greater part associated in 

 their distribution. 



Fig. 141. 



Back view ofpons, bulb, and course of the Fifth 

 Nerre in man. 



18 Tubercula quadrigemina. 



19 Continuation upward of the tract from which 



the Fifth Nerve arises. 



The other references indicate the same parts as 

 in the preceding figure. 



"When the adjoining matter has been care- 

 fully cleared away from the part to which the 

 packets of the nerve are attached, that part ap- 

 pears to be a longitudinal tract of a yellowish- 

 white colour, composed of fibres running in the 

 same direction, and capable of being followed 

 both upward and downward : upward this tract 

 seems continued beneath the superior peduncle 

 of the cerebellum;* downward it descends from 



* Of the nature of the structure continued up- 

 ward from the attachment of the nerve the author 

 is not satisfied : it presents, when cleared, the ap- 

 pearance given to it in fig. 141 , 19, but it is very cine- 

 ritious in character, and he is not prepared to say 

 whether it be a continuation of the tract from which 

 the nerve appears to arise, or a part of the floor of 

 the fourth ventricle at its upper extremity, con- 

 nected to the attachment of the nenre : the mode 

 in which the nerve arises in the bird and the turtle 

 appears to the author opposed to the opinion that 

 the tract to which the nerve is attached is, in them 

 at least, any thing more than a continuation or 

 VOL. II. 



behind the pons into the spinal bulb, and after 

 a short course divides into two cords, one for 

 each column of the spinal marrow (see Jigs. 

 140, 141). At the entrance of the tract into 

 the bulb it is situate deep, before the floor of 

 the fourth ventricle and behind the superficial 

 attachment of the two portions of the seventh 

 pair, which must be separated from each other 

 and displaced in order that it may be ex- 

 posed : externally the tract corresponds to the 

 peduncles of the cerebellum, and is united in- 

 ternally to the cineritious matter of the floor 

 of the ventricle. At the point of attachment 

 the tract presents a somewhat prominent en- 

 largement, (figs. 140, 141, 12,) which the au- 

 thor will venture to call an eminence, though 

 with hesitation, lest it be considered an ex- 

 aggeration, from which the nerve may be held 

 to arise. 



It is said that the nerve may be held to arise 

 from this tract, because, though it be certainly 

 not its ultimate connection with the brain, and 

 though cords can be traced from it to more 

 remote parts, yet the union of the cords at the 

 point, and the attachment of both portions of 

 the nerve to it, seem to mark it as the origin 

 of the nerve ; the change of character too which 

 will be described as occurring at the attach- 

 ment of the nerve, countenances the opinion 

 that the tract is not simply a continuation of 

 the nerve. 



It may be doubted whether the eminence 

 really exist, or whether it be not merely the 

 result of dissection : the author will not insist 

 upon it, but several considerations induce him 

 to consider it real : in the first place, he almost 

 uniformly finds it,* and secondly, it seems to 

 be a common point to the two portions of the 

 nerve and to the other cords, which form part 

 of its encephalic connections ; and lastly, this 

 view is corroborated by the disposition of the 

 same part in other animals ; for a similar ap- 

 pearance will be found, at the attachment of 

 the nerve behind the pons, in other mammalia 

 as well as in man after the separation of the 

 adjoining matter, e.g. in the horse; and it is 

 even asserted by Desmoulins that an eminence 

 may be observed naturally upon the floor of 

 the fourth ventricle, in some animals, at the 

 attachment of the nerve. His statement is : 

 " on observe meme dans les rongeurs, les 

 taupes, et les herissons, un petit mamelon ou 

 tubercle sur 1'extremite anterieure du bord du 

 ventricule ; mamelon, dans lequel se continuent 

 les fibres posterieures de la cinquieme paire, et 

 de 1'acoustique." When the tract has reached 

 the point at which the inferior peduncle of the 

 cerebellum first inclines outward toward the 

 hemisphere, it separates, as has been stated, into 

 two parts or cords, (seejigs. 140, 141,) destined, 

 one, as is already known, to the posterior, the 

 other, according to the author's belief, to the an- 

 terior column of the spinal cord. The course and 

 disposition of these cords are remarkable and 



root of the nerve, but admitting this, he cannot 

 satisfy himself that it is to be regarded in the same 

 light in the Mammalia. 



* The attachment of both the packets must be 

 made out, else the enlargement will not appear. 



I 



