006 



A TEXTBOOK OF PHYSIOLOGY 



aqueous humour passes. The fibres of the ciliary muscle are partly 

 attached to this ligament. 



The Retina is a delicate nerve-film covering the posterior two-thirds 

 of the eye. It ends in front in a notched edge the ora serrata. In 

 the centre of the retina is a round yellowish spot, 1 millimetre in 

 diameter, known as the macula lutea. When viewed in the living 

 eye, however, it is of a deep red colour. It is depressed in the centre, 

 forming the fovea centralis. Just to the nasal side of the yellow 

 spot is the point where the optic nerve leaves the eyeball. It is known 

 as the optic disc, or, since there is no sensation of vision there, the 

 blind spot. Here the retinal artery enters the eyeball, and the retinal 

 vein leaves it. The clinician particularly studies the condition of 

 the optic disc with the ophthalmoscope. Normally, it appears as a 

 circular pink disc, from which the artery and vein radiate out on to 

 a red background. 



FIG. 340. DIAGRAM OF THE RETINA IN MAN. (Redrawn after Lewes-Stohr, from 

 Dahlgren and Kepner.) 



vis. c., Laying of visual cells (rods and cones), the nuclei and processes forming the 

 outer nuclear layer; nv. c., layer of bipolar cells, the inner nuclei of which form 

 the inner nuclear layer; <j. c., ganglion cells, forming the ganglion cell layt-r; 

 nv. /., nerve fibre layer; sup. c., supporting or neuroglia cells. 



Structurally, 'the retina is exceedingly complicated (Fig. 340). It 

 contains (I) the receptor mechanism (the rods and cones); (2) 

 the second (conductor) neuron; (3) the third (conductor) neuron, 

 the elongated processes of which go to form the optic nerve. The 

 cells of these neurons, the interdigitation of their synapses, and the 

 supporting cells, form the many layers of the retina. These are 

 usually enumerated as follows: 



