NERVES OF THE ENCEPHALON. 377 



(Par Quintum) is one of the largest among those that proceed 

 from the basis of the brain, and emerges from the side of the 

 pons varolii, just where it is continuous with the crus cerebelli. 

 It is composed of three roots : an anterior, a posterior, and a 

 middle;* of which the latter is much the largest. 



The middle root is about a line and a half in breadth, and has 

 a passage made for it by the very obvious splitting of the super- 

 ficial fibres of the pons varolii. It is composed of thirty or forty 

 fasciculi, which are divisible into a hundred or more fibres. 

 These fasciculi may be traced into the substance of the Pons 

 Varolii, (but intersected by the transverse fibres of the latter,) 

 in the direction of the fourth ventricle. When they have come 

 near the latter, they may be traced thence into the medulla ob- 

 longata, towards the fissure that exists between the corpus oli- 

 vare and restiforme. It is at this point, that the greater num- 

 ber of the fibres arise; some from the corpus olivare, and others 

 from the fissure. 



The commencement of this root is pulpy and destitute of fila- 

 ments, and is surrounded by grayish substance; but when it has 

 advanced into the pons, it is surrounded by a fine membrane, 

 and is very evidently filamentous. There is a successive in- 

 crease in its size, from its commencement till it is ready to 

 emerge from the pons, when it becomes somewhat contracted, 

 and immediately afterwards increases again considerably in 

 size. It then enters a canal of the dura mater at the fore part 

 of the petrous portion of the temporal bone, and just behind the 

 cavernous sinus. This canal sets but loosely about it at first, 

 but afterwards it adheres to the surface of the nerve. 



The middle root of the nervus trigeminus, in the upper part 

 of the canal of the dura mater, preserves its fasciculated ap- 

 pearance, and many small filaments are interchanged between 

 the fasciculi, so as to make a complex net-work. But, at the 

 lower part of this canal, it is converted into a ganglion of a 

 semi-lunar shape, with its concavity upwards, being about six 

 or eight lines in length, and one and a half in breadth. This body,, 

 called the Ganglion of Gasser, (Ganglion Semi-lunare, Plexus 

 Gangliformis,) is compact, and has its fibres very much matted 



* Santorini, Observ. Anat. Venitia, 1724. Soemmering, de Corp. Hum. Fab- 

 rica, torn. iv. Gall and Spurzheim, Anat. du Cerv. 



33* 



