GENERAL ANATOMY. 



in proportion as they traverse the layers towards the surface, in consequence, 

 apparently, of branches which they give off to be connected with cells in their 

 course. Those which reach the outer gray layer are reduced to the finest 

 dimensions, and form a close network, with which the nuclei and cells are in 

 connection. 



" Besides these fibres which diverge from the central white axis of the con- 

 volution, another set, springing from the same source, converge or rather curve 

 inwards from opposite sides, to form arches along some of the gray layers. 

 These arciform fibres run in different planes transversely, obliquely, and 

 longitudinally and appear to be partly continuous with those of the divergent 

 set which bend round, as already stated, to follow a similar course. All these 

 fibres establish an infinite number of communications in every direction, be- 

 tween different parts of each convolution, between different convolutions, and 

 between these and the central white substance." 



Mr. Clarke then goes on to describe in detail the minuter differences which 

 exist between the structure of the convolutions in different parts of the brain. 1 



Spinal Cord. In the spinal cord, on the other hand, the gray matter is entirely 

 in the interior of the organ, and is collected together into one central mass, 

 while the whole of the white matter is external, and is arranged into various 

 columns and commissures. (See Spinal Cord.) We shall here merely give an 

 account of the intimate structure of the cord, which is condensed from the 

 researches of Mr. Lockhart Clarke. 2 



The white substance of the cord consists of transverse, oblique, and longitudinal 

 fibres, with bloodvessels and connective tissue. 



The transverse fibres proceed from, the gray substance, and form with each 

 other a kind of plexus between the bundles of longitudinal fibres, with which 

 many are continuous; while others reach the surface of the cord through 

 fissures containing connective tissue. Within the gray substance they are 

 continuous with the roots of the nerveSj with the processes of the nerve-cells, 



and with the anterior and posterior 



Fig. 30. commissures. The oblique fibres pro- 



ceed from the gray substance both 

 upwards and downwards : they form 

 the deep strata of the white columns, 

 and, after running a variable length, 

 become superficial. The longitudinal 

 fibres are more superficial, rufi nearly 

 parallel with each other, and form 

 the greater portion of the white 

 columns. 



The gray substance of the cord 

 consists of, 1. Nerve fibres of varia- 

 ble, but smaller average diameter 

 than those of the!columns. 2. Nerve- 

 cells of various shapes and sizes, with 

 from two to eight processes. 8. 

 Bloodvessels and connective tissue. 

 Each lateral half of the gray sub- 

 stance is divided into an anterior 

 and posterior horn, and the tractus 



Transverse section of the gray substance of the spinal 

 cord, near the middle of the dorsal region. (Magnified 

 13 diameters.) 



intermedio-lateralis, or lateral part of the gray substance between the anterior 

 and posterior cornua. 



1 See Mr. Clarke's summary of his researches on this subject in Maudsley on the Pathology 

 and Physiology of Mind, pp. 60-63. 



2 Phil. Trans., 1851-1853, part iii. ; 1858 part i. ; 1859 part i. ; 1862 part ii. 



