504 JULIA B. PLATT. 
ramus ophthalmicus profundus to that segment of the brain 
which supplies motor fibres to the mandibular somite. 
Part of the sensory skin covering the mandibular somite sends 
its fibres to the brain by the same root. 
At a slightly later stage in the development of the embryo, 
a band of sensory epithelium on both premandibular and 
mandibular segments, which first sent its fibres to the brain in 
the second (mandibular) segment, now sends them by the ramus 
ophthalmicus superficialis facialis to that segment of the brain 
which supplies the motor fibres of the third and fourth 
somites. 
Again, the intersegmental sensory ridge above the hyo- 
branchial cleft gives rise to two sense-organs lying primarily 
in the same transverse line. One of these organs, the ear, 
sends its sensory fibres to the brain segment which supplies 
the motor fibres of the third and fourth somites, while the 
lower sense-organ in the transverse line sends fibres to the 
brain in the segment supplying motor fibres to the fifth, 
glossopharyngeal, somite. 
The sensory epithelia on the vagus segments send a large 
part of their fibres to that segment of the brain which gives 
rise to the motor root of the glossopharyngeus; part of the 
fibres, however, are distributed to the brain in the first vagus 
segment. 
Behold the heterogeneous mixture, which omitted facts 
would still further complicate; and yet we are told that there 
is a segmental value in the dorsal nerve-root ! 
Each primitive ganglion may be, indeed, a segmental struc- 
ture, so also is the motor nerve, but the value of that ana- 
lytical division of the several cranial nerves which ascribes a 
separate segmental root to each sensory branch is not ap- 
parent. 
The “root”? of the ophthalmicus profundus is primarily 
supplied by part of the skin covering two or more segments— 
the mandibular, preemandibular, and other anterior segments, 
™ ““h there be. The “root” of the ophthalmicus super- 
' I regreycialis is supplied by fibres from the same sensory area 
