soeilons. Microscopic work oitlior on ilio Lrain oi' tlie 

 ])t'ripheral nerves only is iiiadecjiiate, and dissection, as a 

 moans of rosearcli, has l)ut a very doubtful value. Tlic 

 only fish which has heen thoroup^hly invest ig-ated according' 

 lo tlie coniponeui theory is Menidia — in an im])oitani 

 work puhlished recently by ('. -T. Heriick, who truly 

 remarks: " Tntil each component can be isolated and 

 treated as a morpholoo-ical 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 

 Ihe cranial nerves of the Plaice are as f(dlows : — 



1 . General Cutaneous or Somatic Afferent System. — 

 These fil)res, which undcnibtedly correspond to th(^ 

 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 Grasserian 

 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 

 distril)uted 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 

 Prion at ux (Morrill). 



•2. Somatic Efferent System.— Represented l)y the 

 heavily myelinated eye muscle nerves (iii., iv. and vi.). 

 This system is of course largely present in the so-called 



