102 SENSE ORGANS. 



probably not yet be developed, and this coat may be difficult of 

 detection. The retina comes next as the inner covering of the 

 eye, and may exhibit two distinct layers continuous with each 

 other in front (line where the infolding has occurred) if the eye 

 is young enough. The outer thinner portion, probably containing 

 pigment, will form later the pigmentary layer of the retina. 

 Internally to this is the retina proper, i.e., that portion which 

 subsequently is alone connected with the optic nerve. Trace the 

 optic nerve into connection with the retina and note its central 

 artery. As it is not always possible to ensure a foetus of the 

 younger age, at which 1he simpler evolution of the eye-cup from 

 the brain vesicle is best seen, this description is intended to 

 apply equally to older preparations. 



Corneo-sclerotic junction. Dog or Cat. V.S. (p. 8, s. 22 and 24, 

 c. P.,m. B.) (Z) and (H) Externally the cornea is covered with 

 stratified (conjunctival) epithelium, the innermost cells of which 

 are columnar ; beneath this is the corneal substance of dense 

 fibrous tissue, amongst the layers of which spindle-shaped 

 corneal corpuscles are disseminated. On the inner surface 

 there is a homogenous membrane internal elastic lamina 

 covered by a single layer of flat cells. The junction of cornea 

 to sclerotic is indicated by the occurrence of the pigment 

 and blood vessels of the sclerotic. Internally to this is the 

 attachment (Lig. annulare bulbi) of the choroid, which is the 

 pigmented and vascular coat of the eye. The choroid has 

 three subdivisions : The Iris in section hangs into the anterior 

 chamber, and the surface turned towards the corea is covered 

 by a single layer of densely pigmented cells. Throughout its 

 substance there are branched cells and blood vessels. Towards 

 the free edge bundles of plain muscle are added (Sphincter). 

 Beneath the epithelium of the inner surface there is a fibrous 

 layer free of pigment. The pectinate ligament is the frayed 



