112 
sections. Microscopie work either on the brain or the 
peripheral nerves only is inadequate, and dissection, as a 
means of research, has but a very doubtful value. The 
only fish which has been thoroughly investigated according 
to the component theory is J/enzdia—in-an important 
work published recently by C. J. Herrick, who truly 
remarks: ‘‘ Until each component can be isolated and 
treated as a morphological unit, and then unravelled in its 
peripheral courses through the various nerve roots and 
rami—until this is possible, no further great advances 
in cranial nerve morphology can be looked for even among 
the lower vertebrates, still less in man.” 
The five systems of fibres which variously compose 
the cranial nerves of the Plaice are as follows :— 
1. General Cutaneous or Somatic Afferent System.— 
These fibres, which undoubtedly correspond to the 
cutaneous fibres of the spinal nerves, are derived from 
continuations of the dorsal horns of the spinal cord, which 
form two longitudinal bundles in the medulla known as 
the spinal vth tracts. These fibres in the Plaice leave the 
brain by the roots of two cranial nerves only—the vth and 
the xth. In the former case their ganglion is the Gasserian 
ganglion, in the latter the jugular ganglion. The 
cutaneous fibres in the facial nerve are distinctly derived 
from those of the fifth. The fibres of this system are 
distributed generally to the skin, and do not end in any 
specialised dermal sense organs. Hypertrophy of this 
system produces a corresponding hypertrophy of its centre 
in the central nervous system, as witness the remarkable 
lobes at the anterior extremity of the spinal cord of 
Prionotus (Morrill). 
2. Somatic Efferent System.—Represented by the 
heavily myelinated eye muscle nerves (i11., iv. and vi.). 
This system is of course largely present in the so-called 
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