1863.] 719 



as regards the convolution, and with different degrees of obliquity. 

 While the bundles themselves are by this means reduced in size, their 

 component fibres become finer as they approach the surface, in con- 

 sequence, apparently, of branches which they give off, to be con- 

 nected with cells in their course. When they arrive at the outer grey 

 layer, they are reduced to the finest dimensions, and form a close 

 network, with which the nuclei and cells are in connexion*. Through 

 this layer, however, many of them pass in straight lines, and, in 

 company with processes from some of the cells, traverse the next 

 outer and white layer, in which part of them turn round the circum- 

 ference of the convolution part run longitudinally and with various 

 degrees of obliquity, but parallel with the surface, decussating with 

 the former others appear to form loops by returning to the grey 

 lamina from which they proceed while the rest continue their 

 vertical course, crossing each other at different angles, and reaching 

 the surface, where they become continuous with the compact and 

 thin stratum of fibres which forms the first layer of the convolu- 

 tion, and is in immediate connexion with the pia mater. 



While the bundles of fibres diverge on all sides from the central 

 stem of white substance, another system of fibres, springing from 

 each side of the base of the stem, curve inward and form a beautiful 

 arch over its summit, where they decussate each other, and partly 

 constitute the innermost pale layer. The fibres of the stem itself are 

 crossed transversely and obliquely by a variable number of others of 

 different diameters ; and in longitudinal sections (that is, in sections 

 made in the length of the convolutions) these transverse and oblique 

 fibres are frequently seen to increase in number toward the base of 

 the white substance, where they decussate each other at every pos- 

 sible angle. 



Such is the structure of the convolutions at the extremity of the 

 posterior lobe, in which the laminated appearance is most marked. 

 In almost all other convolutions, however, eight laminse, although 

 sometimes indistinct, may be brought into view by means of solution 



* This network in the grey substance between the cells and fibres was, I be- 

 lieve, first noticed by myself in my article on the Structure of the Olfactory Bulb, 

 &c., in Siebold and Kolliker's Zeitschrift, 1861, Bd. xi. Heft 1, plate v. fig. 6; 

 and subsequently in my memoir " On the Development of the Spinal Cord," Phil. 

 Trans. 1862, p. 925, note. 



3E 2 



