NEAL: NERVOUS SYSTEM IN SQUALUS ACANTHIAS. 298 
which develops in precisely the same way as do ventral (medullary) 
spinal nerves, possesses a much elongated motor nucleus in the ven- 
tral horn of the medulla, and innervates pre-otic (possibly also in the 
embryo post-otic) musculature (musc. rectus posterior). These facts 
seem significant in dealing with the question of the primitive metameric 
relations of this nerve, 
At a stage when the embryo has a length of 17 mm. (78-80 somites) 
the ramus opthalmicus superficialis V (Plate 4, Fig. 20; compare Fig. 21) 
appears as a fibrillar nerve with peripheral nuclei extending from the 
Gasserian ganglion just dorsal to the point of exit of the fibres of the 
r. ophth. profundus V, and passing anteriorly close to the ectoderm 
below the r. ophthalmicus superficialis VII. The relations of these two 
ophthalmic nerves are therefore such that they have usually been re- 
garded as of the same morphological value, i. e. as rami cutanei dorsales 
of nerves V and VII respectively. Yet an interesting relation of proto- 
plasmic processes from the r. ophth. sup. V with the myotome of the 
second somite, such as is represented in Plate 8, Figure 60, has been 
called to my attention by Miss Platt. Since at this stage of develop- 
ment the fibres of the trochlearis have not appeared, the inference would 
seem warranted that motor impulses may have primitively passed to this 
myotome (muse. obliquus superior) through the fibres of the r. ophth. 
sup. V. Such a supposition, however, is greatly diminished in force, 
and in my opinion rendered untenable, by the fact that in embryos of 
19 mm. — therefore before the fibres of the trochlearis are in connection 
with the m. obliquus superior — the r. ophth. sup. V shows no longer 
connection with this muscle (Figure K). The fibres of the anterior root 
(portio minor) of the trigeminus nerve may now be traced from their 
origin through the Gasserian ganglion into the mandibular arch, where 
they give off fibres both to the muscles of the arch and to the skin of its 
anterior and lateral surface. The fibres appear in large part motor. 
Since this is the only motor branch of the V, it would follow that the 
posterior root (portio major) includes chiefly, if not entirely, sensor 
fibres. It would moreover follow that encephalomere III is chiefly, if 
not wholly, connected with motor fibres, which may be traced forward to 
a considerable distance in it to the neuroblasts in the lateral horn, with 
which they are in connection, while encephalomere IV has chiefly sensory 
fibres in connection with it. Mitrophanow’s (’93, p. 178) evidence is, 
however, considerably at variance with that just stated. He finds that 
in an embryo Squalus of 18 mm. “la racine du nerf trijumeau est large 
