78 PATTEN. [Vol. I. 



nected at their distal extremities with a circular fibril enclosing 

 the whole (7.)' °'' ^ nerve-fibre follows the cell-wall for some 

 distance, giving off at intervals smaller, lateral branches, and 

 finally becoming so minute as to disappear (5".). 



The outer prolongations of the ganglionic layer form, beneath 

 the septal membrane, a mass of free fibres, which were mistaken 

 by Carrilre for nucleated cells, and by Hensen for fibres pulled 

 out of the retina by shrinkage. The layer of free nerve-fibres 

 is, however, a normal condition, and is necessarily so in order 

 to give the lens space for focal adjustment without injury to the 

 retina, 



A system of circular fibres surrounds the periphery of the 

 inner face of the retina, forming a meinbrana circidaris. 



Beneath the rods there is a thin layer of a vitreous substance 

 forming a net-work, the meshes of which constitute a hexagonal 

 crown for the inner end of each rod. On the periphery of the 

 retina the vitreous net-work is transformed into a thin plate, 

 pierced by numerous and irregularly-shaped holes. 



The argentea is formed by the modification of two cell layers 

 into refractive membranes. Each membrane is composed of 

 minute square plates, whose edges are bevelled in such a man- 

 ner that their outer faces are smaller than the inner, which rest 

 upon the undifferentiated, under surface of the membrane by 

 which all the plates are held together. In passing inwards the 

 membranes become thinner, less distinct, and refractive, while 

 the plated structure entirely disappears. The thick outer layer 

 of ^Q argentea in the adult never contains nuclei, although 

 one or two may occasionally be found in the inner layer. 



The tapetum, the red-pigment layer of previous writers, 

 usually consists of a single layer of cells, decreasing in thick- 

 ness from the axial part of the eye toward the periphery, and 

 terminating with the argentea at the entrance into the retina of 

 the fibres from tke axial branch of the optic nerve. 



The thickened central part of the outer layer of the septum, 

 a little to one side of the optic axis, is perforated by the gangli- 

 onic nerve-branch. The peripheral part, gradually diminishing 

 in thickness toward the edge of the retinal sac, consists of 

 nucleated connective-tissue cells modified into circular fibres. 



The inner layer of the sclerotica is marked with short par- 



