CHAPTER X 

 SCYLLIUM CANICULA (continued) 



Nervous System and Sense Organs. 



Nervous System and Sense Organs. 



Again, as in the frog, we may divide the nervous system 

 and its associated sense organs for convenience in description into 

 Central nervous system, Peripheral nervous system and Sense organs. 

 The central nervous system, consisting of the brain within the 

 cartilaginous cranium and the spinal cord enclosed in the' neural 

 canal, is enclosed in two membranous meninges, an outer dura mater 

 and an inner pia mater as in the frog. 



Brain. 



The brain does not occupy quite the whole of the space 

 within the cranium, and the interspaces are filled up with a viscid 

 fluid which becomes semi-gelatinous in preserved specimens. 

 Despite the difference in external appearance, owing to the different 

 size and proportion of the parts, the brain in Scyllium is composed 

 of essentially the same parts as in Rana. 



At the front end we find the telecephalon or cerebrum, which 

 appears as a smooth globular mass at the extreme end of which is a 

 groove. Although it does not appear so from the outside it is, 

 nevertheless, a paired structure, and within it there are two distinct 

 lateral ventricles separated from each other by a median partition 

 of nervous tissue. The two olfactory lobes, stout oval masses, are 

 borne, one on each side of the anterior aspect of the telencephalon, 

 on stout stalks, the olfactory peduncles. They are closely adherent 

 to the cartilaginous hinder portions of the olfactory capsules through 

 which numerous fibres, collectively constituting the olfactory nerve, 

 pass. The latero- ventral walls of the telencephalon are thickened 

 by masses of nervous tissue corresponding with the corpora striata 

 of higher forms, although they are not so well defined. 



The cerebrum passes over insensibly into the succeeding narrower 

 part of the brain, namely, the thalamencephalon, whose thickened 

 ventro-lateral walls constitute the optic thalami. This part is 

 markedly hollow, owing to the presence in it of the enlarged third 



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