THE CRANIAL NERVES OF SCYLL1UM. 95 



clearly seen to have occurred on comparing fig. 4 -with fig. 1. We 

 believe that what really happens is that about the commencement of 

 stage K the nerve acquires a new and secondary connection with the 

 brain at the point (v /3) opposite the projection already noticed ; that 

 the primary attachment (v a) is lost ; and that the part of the nerve 

 left above the secondary root rapidly diminishes and ultimately 

 disappears altogether, the slight dorsal projection already noticed in 

 fig. 4 being the last rudiment of it. As our arguments in support of 

 this view depend almost entirely on our own observations on the 

 development of the roots of the seventh nerve, we postpone further 

 consideration of the point till a later portion of this paper. 



At the commencement of stage k then, the fifth nerve arises about 

 half way up the sides of the hind-brain by a single large root in which 

 ganglion cells are abundant, and opposite to which there is a well- 

 marked external bulging of the walls of the brain j 1 beyond this root 

 the nerve expands suddenly into a very large ganglionic swelling, the 

 future Gasserian ganglion. 



Before the close of stage k additional roots appear ; a long, slender 

 process runs forward from the antero-superior angle of the Gasserian 

 ganglion, and becomes connected with the brain some distance in front 

 of the main root ; in addition to which one, two, or more roots of a 

 similar kind appear in intermediate situations. 



These anterior roots of the fifth nerve are well shown at the next 

 stage (l) in fig 10, v y, which shows that the fifth nerve at this time 

 arises from the brain by three distinct roots, of which the posterior 

 one is much the largest, and is the ganglionic root (v /3) of fig. 4, while 

 the two anterior slender non-ganglionic roots are the new ones. We 

 have studied these roots very carefully, but have been unable to 

 determine with certainty whether they are outgrowths from the brain 

 to meet the ganglion, or from the ganglion towards the brain ; our 

 observations, however, though inconclusive, tend very strongly towards 

 the latter of the two alternatives. It has also occurred to us that 

 these new roots may possibly be the original primary root of origin 

 (v a, fig. 1), which, after losing its original attachment, has acquired 

 a new one lower down ; however, though the dates of the disappearance 

 of v a and appearance of Vy agree fairly well with this hypothesis, 

 we have yet no actual observations in its favour, and do not wish to 

 lay stress upon it. 



1 Marshall, loc. cit., p. 84. 



