CHAPTER XIII 

 LEPUS CUNICULUS (continued) 



The Nervous System and Sense Organs The Mammalian Brain. 



As in the lower forms, we find the whole of the central 

 nervous system provided with a series of protective coverings, the 

 meninges. The outermost of these is the dura mater, a tough fibrous 

 membrane which lines the cavity of the cranium and neural canal. 

 This dips down into the fissure between the cerebral hemispheres 

 forming a sort of median membranous partition, the falx cerebri ; 

 it also dips down in a similar way between the hinder end of the 

 hemispheres and the cerebellum, thus giving rise to a transverse 

 partition, the tentorium. In some mammals one or both of these 

 folds may become ossified, and so give rise to thin bony plates 

 attached to the inside of the cranium and dipping down into the 

 fissures of the brain. Underlying the dura mater is a small sub-dural 

 lymph space, and then a delicate arachnoid membrane, which is 

 composed of a close felting of connective tissue. Finally, we have 

 the innermost membrane, the pia mater, also delicate and extremely 

 vascular. This invests closely the whole of the nervous matter 

 dipping down into all the grooves of the brain and spinal cord. 



The central nervous system is divisible into the brain and 

 spinal cord, and the nervous tissue of which it is composed is divisible 

 into grey matter and white matter as in all vertebrates. In the 

 brain the former is on the outside, constituting the cortex, and the. 

 latter is inside, while in the spinal cord their positions are reversed. 

 The grey matter is mainly composed of nerve cells with non-medul- 

 lated fibres, and the white is formed entirely of fibres most of which 

 are medullated. 



Brain. 



The brain of the rabbit is small and somewhat highly 

 specialised, so that for more detailed investigation it is better to 

 take the brain of a larger animal such as the sheep, and only 

 consider the main outlines of its structure in the rabbit. The same 

 main divisions of the brain that we have already seen in Scyllium 



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