374 SPECIAL HISTOLOGY. 



only by their beautiful vesicular nuclei ; whilst another por- 

 tion, forming an almost continuous layer on the inner side, 

 are of larger size (0006 — 0016"'). These cells are usually 

 pyriform or rounded, or occasionally prolonged into 3 — 5 angles ; 

 and most of them, perhaps all, are furnished with pale pro- 

 cesses like those of the central nerve-cells — which were first 

 noticed by Bowman {' Lectures/ &c, pp. 84 and 125), and 

 afterwards also described by Hassall, Corti, and myself. 1 

 The processes occur either single or in numbers varying 

 from two to six and more ; are at first as much as , 002" / 

 wide, but in their further course continually diminish in size, 

 under repeated divisions, till they are reduced to fine filaments 

 of scarcely 0004"' in diameter, which, in isolated cells, termi- 

 nate in torn ends. In every case in which I have noticed 

 these nerve- cells distinctly in situ, their processes were given 

 off towards the exterior, and afterward? in their further course, 

 without entering the granular layer, appeared to be curved, in 

 order to ramify in the grey nervous layer itself. The nuclei of 

 these nerve-cells, which behave towards reagents like those of 

 the cerebrum, measure 0*003 — O'OOS'", and usually present a 

 very distinct nucleolus. 



4. On the inner aspect of the layer in question we find the 

 expansion of the optic nerve (d). This nerve, after quitting 

 the chiasma (concerning which vid. p. 44i, vol. I) and till it 

 reaches the eye, presents the same conditions as a common 

 nerve ; its dark-bordered fibres, 00005 — 0*002'" in diameter, 

 much disposed to become varicose, and between which, ac- 

 cording to Hassall, nerve-cells would also seem to occur, 

 but which I have not yet noticed, form polygonal bundles, 

 0'048 — 0064'" thick, surrounded by a neurilemma of the 

 usual kind. When the optic nerve has reached the eye, 

 its sheath is lost in the sclerotic, which tunic is perforated 

 for the entrance of the nerve by a funnel-shaped opening, the 

 narrower part being inward ; and the internal neurilemma also 

 ceases on a level with the inner surface of the same tunic, 

 where it may be artificially displayed, as a cribriform lamella 

 (lamina cribrosa of authors), so that the fibres of the optic 



1 [Pacini appears to have been the first to perceive the existence and true nature 

 of the caudate cells in this layer of the retina. (' Sulla tessitura int. dell. Retina,' 

 1844, p. 32.)— Eds.] 



