96 PROF. MARSHALL AND MR. SPENCER. 



These anterior roots which, during stage l, may be three or more 

 in number, appear in the later stages to be very constantly reduced to 

 two, one of which is the most anterior of the original roots while the 

 other appears to be formed by the fusion of the intermediate ones. 



This condition at stage N is well shown in fig. 11, v y. At a stage 

 between o and p (fig. 14, vy) they are rather less conspicuous owing 

 to the interval between them and the secondary root (v /3) being 

 filled up by dense tissue. They are clearly recognisable in the adult, 

 and form, as will be noticed more fully further on, the first or anterior 

 root of the fifth nerve of zootomists. 



B. The tranches of the fifth nerve. — The Gasserian ganglion is, from 

 its first appearance, wedged in between the dorsal ends of the second 

 and third head cavities in the same manner as is the ciliary ganglion 

 between the first and second (fig. 10). From the Gasserian ganglion, 

 at stage K, two nerves arise ; of these, one, which runs straight down 

 between the second and third head cavities, and then along the 

 anterior border of the mandibular arch in front of the ventral portion 

 of the cavity in the latter, is the mandibular branch ; and from this, 

 a considerable distance below the ganglion, a small anterior branch — 

 the maxillary nerve — is given off. The second branch from the 

 Gasserian ganglion arises from its anterior inferior angle, runs along 

 the top of the first head cavity and joins the ciliary ganglion ; it is 

 the communicating branch between the fifth and third nerves already 

 mentioned, and forms the proximal part of the ramus ophthalmicus 

 profundus of zootomists. 



At stage l a slender branch arises from the anterior superior angle 

 of the Gasserian ganglion ; this is the ophthalmic branch of the fifth 

 (fig. 10, v a) which runs forward through the orbit dorsal to all the 

 eye muscles, giving off branches to the neighbouring parts in its 

 course and terminating in the skin of the fore part of the head. One 

 other nerve in connection with the fifth remains to be noticed ; this is 

 the connecting branch (iV.c'., fig. 10) between the 'fifth and seventh 

 nerves : this is present at K, at which stage as well as at L it forms a 

 very stout though short nerve, running forwards and downwards from 

 the seventh nerve, over the top of the third head cavity, to join the 

 lower part of the Gasserian ganglion. 



The branches of the fifth nerve at stage n are well seen in figs. 11 

 and 12, which have been constructed so that each of them may show 

 the whole course and distribution of certain nerves : the' outlines of 



