494 THE BKAIN OF MAMMALS, BY TH. MEYNERT. 



These fibres, arising from the raphe', decussate and run forwards 

 as its fibrse rectse, forming arches with their convexity upwards, 

 and pass (curving over the facialis abducens nucleus) uninter- 

 ruptedly into the roots of the facial nerve (fig. 254, on the right 

 side, where they appear as light fasciculi in front of the dark area 

 0). In consequence of this curve their continuity with the root 

 is only visible in the uppermost planes of section of the region oi 

 origin of the nerve ; in those made at a lower level the crown of 

 the arch is removed. A few of these descending root fasciculi 

 do not run within the raphe, but through the motor area, and, 

 decussating with the fibrse arcuatse, become associated with the 

 other roots of the facial (fig. 254, on the right side, between R 

 and 6). It naturally remains uncertain whether the fasciculi 

 have a common origin say, in the lenticular nucleus with 

 those roots of the facial which run as fibrse rectse of the raphe. 



2. Roots of the facial, the nucleus of origin of which is 

 situated at the level of the plane of emergence. These fasciculi, 

 though not admitted by Deiters, arise from the nucleus common 

 to the abducens and facialis, and indeed from its upper half 

 alone, so that it is not unlikely that the connection of the facialis 

 with this nucleus may be called in question when sections 

 are made through a somewhat lower plane. As far down, how- 

 ever, as this connection can be traced, the root fasciculi of the 

 facial emerge from the nucleus in a very characteristic manner, 

 their expansion corresponding exactly with the height of the 

 nucleus itself (fig. 254, on the left). 



3. Roots of the facial, the nucleus of origin of which is 

 situated below the plane of emergence. Ascending roots. 

 Dean and Deiters have given independent descriptions of the 

 course of these fibres, and sufficiently correct, so far at least as 

 can be ascertained from the unfinished work of the latter. 

 Clarke has also thoroughly investigated their relations, and 

 errs only in regarding the superior olivary body as their nucleus 

 of origin, instead of the inferior facial nucleus, which he has 

 mistaken for the motor nucleus of the fifth. Their nucleus 

 origin is the anterior (inferior) nucleus of the facial, a cluster 

 of slender multicaudate nerve corpuscles (of about 60 /u long 

 and 21 JJL broad), which, extending into the region of the 

 abducens-facialis nucleus, has a length of 3 '5 millimeters, and 



