272 



FIFTH I'AIR OF NERVES. 



gin ; it is then situate in the angle formed by 

 the three peduncles of the cerebellum at their 

 junction with the hemisphere; behind the 

 middle, beneath the superior and above the in- 

 ferior, and before, or in common language, be- 

 neath the floor of the fourth ventricle. Thus 

 far the course of the nerve may be ascertained 

 without much difficulty ; it is probably the 

 same point to which Santorini had traced it, 

 as described in his ' Observationes Anatomicae,' 

 in 1724, and from which Soemmerring has 

 more expressly stated it to be derived, in his 

 work ' De corporis humani fabrica,' pub- 

 lished 1798, in which he states " that it ap- 

 pears to arise almost from the very floor of the 

 fourth ventricle." * At the point last described 



Fig. 140. 



Lateral view of the pans, spinal bulb, and course of 

 the Fifth Nerve in man. 



\ Pons Varolii. 



2 Spinal bulb. 



3 Olivary body. 



4 Spinal cord. 



5 Superior peduncle of cerebellum. 



6 Cut surfaces of middle ditto. 



7 Inferior peduncle of cerebellum. 



8 Cut surface of crus cerebri. 



9 Ganglion of Fifth Nerve reversed. 



10 Ganglionic portion of the nerve. 



11 Non-ganglionic portion of Fifth Nerve. 



11 Roots of non-ganglionic portion. 



12 Eminence at the insertion of both portions of 



the Fifth Nerve. 



13 Fasciculus to anterior column of spinal cord, 



14 Fasciculus to posterior column. 



15 Auditory nerve. 



16 Portio dura. 



17 Posterior roots of superior cervical nerves. 



* Santorini, however, appears to have followed 

 the nerve out into the spinal bulb, though, as will 

 be seen, he did not succeed in determining its real 

 and ultimate connection. 



the greater packet is attached to the side of the 

 medulla oblongata. The point of attachment 

 is very close to the interior of the fourth ven- 

 tricle, being separated from it only by a thin 

 lamina, which is little, if any thing, more than 

 the " epithelium" of Heil : it is situate in the 

 angle formed by the peduncles of the cerebel- 

 lum, behind the middle one, by the outer 

 margin of the pons, and posterior to it, and 

 above its lower one : it is also superior to the 

 attachment of the auditory nerve, separated 

 from it by an interval of some lines. 



We shall, in the next place, direct attention 

 to the course and connection of the lesser 

 packet of the nerve. 



In none of the authorities which the author 

 has had an opportunity of consulting, has he 

 found a particular origin assigned to the lesser 

 packet. By most anatomical writers it is over- 

 looked; J. F. Meckel states that it can be 

 traced a certain way into the crus, but he 

 goes no further; Mayo asserts that the lesser 

 portion arises close upon the greater, and, in a 

 sketch of the origins of the nerves given by him 

 in his Physiology, it is represented traversing 

 the crus cerebelli, as a single fasciculus, above 

 and behind the greater, and attached to some 

 part above that from which the greater is re- 

 presented to arise : but still the origin is not 

 denned, and it is manifestly intended to be 

 distinct from that of the greater packet. 



The author has succeeded, as it appears to 

 him, satisfactorily in tracing both the roots of 

 the lesser packet to a destination for which he 

 was not prepared ; at setting out he expected 

 to have found the origin of the lesser different 

 from that of the greater packet, and to have 

 followed it to a prolongation of the anterior 

 columns of the spinal cord, as has been stated 

 by Harrison ;* it was therefore with surprise 

 that, after a patient dissection, he succeeded in 

 tracing both its roots to the same point, to 

 which the greater packet is attached, behind 

 the middle crus of the cerebellum (see. jig. 140, 

 12); both the roots traverse the crus, as the 

 greater does, the inferior very frequently in 

 company with and internal to the greater 

 packet, or separated from it by a very thin 

 stratum of the substance of the crus, the 

 superior near to the superior surface of that 

 part, and separated from the greater packet by 

 an interposed stratum of two or more lines; 

 the course of the latter is so near to the surface 

 of the crus, that it can frequently be traced for a 

 considerable way by the eye without dissec- 

 tion : they present, in their mode of traversing 

 the crus, two remarkable varieties ; in some in- 

 stances the fasciculi, of which they are com- 

 posed, are separated from each other and even 

 interlaced with those of the crus, and in such 

 the pursuit of them is intricate and difficult ; 

 in others they pass in two distinct packets, and 

 in these they are more easily followed. As 

 they proceed they approach the greater packet, 

 so that the interval between them and it gradu- 

 ally diminishes, and having traversed the crus, 

 they are both attached below and behind it to 



* Dublin Dissector. 



