58 GRAY SUBSTANCE OF THE TRAPEZIUM, 



CHAPTER III. 



THE FACIAL NUCLEUS AND KOOTS. 



The coiu-sc pursued by the facial nerve is so exceedingly distinct in most of the 

 mammalia, that we are surprised to meet with difficulty in tracing the roots to their 

 ultimate destination. Schroder van der Kolk has indeed stated that among all the 

 nerves of the medu.lla, there is not one, the origin of which is so difficidt to define 

 with certainty as the facial.^ As is the case with the.auditory, the facial in man, 

 especially in its outer part, is "pressed slightly downwards by the great thickness of 

 the pons Varolii, but in those mammalia in which the pons is but slightly developed, 

 the facial pursues an almost directly transverse course, so that the fibres can often 

 be followed inwards as far as the floor of the ventricle. 



The facial enters the medulla on the inner side of the caput cornu, and runs in a 

 curving course directly inwards and forwards to the fasciculus teres, Avhich is, as 

 shown above, an upward continuation of the column of large, multipolar cells with 

 which the roots of the hypoglossal were connected lower down. As pointed out by 

 Stilling,^ the roots of the facial generally form a single bundle, though we some- 

 times find them separated into two or three fasciculi (Figs. 13, 14, Plate IV), 

 forming thereby a remarkable exception to most other nerves. 



Stilling has also noticed a remarkable difference between the upper and lower 

 portions of the facial roots. The lower portion terminate in the nucleus, while 

 the upper roots, without entering the nucleus, pass to the raphe where they decus- 

 sate with their fellows from the opposite side. In this course they inclose a bundle 

 of fibres which Stilling has considered to be roots of the trifsicial, but I cannot 

 discover that the column has any connection with this nerve. In the upper portion 

 of the facial he found no remains of the nucleus, and came to the conclusion that a 

 part of the fibres from this portion of the root turn downwards entering the under- 

 lying nucleus, while another portion pass downwards through the raphe to the 

 columns of the spinal cord.^ This difference between the upper and lower portions 

 of the facial course is very conspicuous in the sheep and cat, as well as in man, the 

 nucleus disappearing almost entirely in the upper portion, and we can at the same 

 time trace the fibres from the facial, passing directly to the raphe. As long as the 

 nucleus is persistent many of the fibres of the facial terminate abruptly, just outside 

 the nucleus, that is, they are cut off, as seen in Plate XVI, Fig. 44, the inward 

 course of the fibres from this point being slightly ascending. 



Sometimes a portion of these fibres escape being cut off' by the plane of section 



» Medulla Oblongata, 109. ^ Pons Varolii, 39. ^ I. c. 38. 



