384 BIOLOGY. [Book vr. 



has been remarked at the same time that the cells, probably 

 sensitive, are of smaller dimensions. 



But the cells of the spinal marrow are not merely solidarifeed 

 among themselves : they are also solidarised with the central 

 cells. In what concerns the anatomical relations of the spinal 

 marrow and of the brain, and also the repartition in the ence- 

 phalon, of the cells, and of the fibres, we are indebted to the 

 brilliant labours of Dr. Luys for a picture of the whole subject 

 as simple as it is fascinating.^ 



According to this anatomist all the sensitive fibres of the 

 spinal marrow, whether they have or have 'not encoun- 

 tered on their passage the cells of this first centre, lead into, 

 first of all, two masses of cells, situated at the inferior part of 

 the brain, the optical layers [Thalami nervorum opticoruni]. 

 Then having passed through this secondary centre, they 

 radiate toward the surface of the brain, the grey covering 

 of the circumvolutions. This covering is formed of numerous 

 layers of triangular cells, superposed by veins, like geological 

 strata, having all theii- ridges at high point and being all 

 connected by fibrous points of u^nion. 



The sensitive fibres, radiated from the optical layers, traverse 

 from below to above all these cortical layers, to reach the more 

 superficial strata, formed of cells analogous by their volume to 

 the sensitive cells of the spinal marrow. 



Beneath these layers of small cells, we find beds, superposed, 

 of cells more or less voluminous in proportion to thejr distance 

 from the periphery of the brain. The last strata, the deepest, 

 are constituted by voluminous cells, analogous to the cells, 

 called motory, of the marrow. 



From these last cells set forth descehding fibres, which all 

 converge towalrds two cellular masses, situated also toward the 

 base of the brain, in the vicinity of the optical layers. These 

 masses of grey substance have been called in anatomy striated 



^ ,T. Luya, Sech. sur le Syst. Mrv. Ciribro-spinal, Paris, 1865. 



