552 



PHYSIOLOGY 



LEFT RETINA 



t'lCMT RETINA 

 < I 



which travel round under the crura cerebri and then divide to end in cells 

 in three different nuclei, (a) the anterior corpus quadrigeminum, 

 (6) the external geniculate body and (c) the pulvinar. The optic nerve 

 contains four different sets of fibres : (1 ) those which convey visual impressions 

 to the brain; (2) those going to the pupillomotor centres ; (3) those which 

 come down from the brain to the retinae, the so-called retinomotor fibres, 

 which may have trophic fibres associated with them ; (4) nerves travelling 

 from one retina to the other. The courses of these separate fibres must now 

 be traced. 



(1) From each retina three 

 separate bundles of visual fibres 

 arise: (a) those from the right 

 halves of the retinae, which join 

 at the chiasma and travel to 

 the brain via the right optic 

 tracts ; (b) those from the left 

 halves of the retinae which travel 

 via the left tracts ; and (c) those 

 from the foveae centrales (in man 

 and monkey only) which partly 

 travel via the tract of their own 

 side and partly cross to that 

 of the other. The right optic 

 tract thus contains all the visual 

 fibres from the right sides, 

 and half those from the centres 

 of the two retinae, which travel 

 to the right occipital cortex 

 through the pulvinar and exter- 

 nal geniculate body of that side. 

 The left tract travels to the left 



Fio. 282. Diagram showing the probable 

 relations between the parts of the retinae 

 and the visual area of the cortex. (SCHAFER.) 



occ i p ital cortex in a similar mail- 



ner. These connections are 

 represented diagrammatically in Fig. 282. 



(2) The pupillomotor impulses travel up without crossing, as I have 

 already described on page 510, to the anterior corpora quadrigemina (see also 

 Fig. 203 and page 406). 



(3) Nothing is I believe known as to the fate of these so-called retino- 

 motor fibres ; some of them may, in fact, be trophic or vaso- constrictor fibres. 



(4) The function of these inter-retinal fibres are not known definitely. 

 It has been suggested that they cause changes in one retina when light 

 falls on the other, as for example cone movement. It has also been sup- 

 posed that the sympathetic inflammation which occurs in one eye after 

 certain injuries to the other, is due to impulses which have travelled via these 

 nerves ; lastly binocular contrast and after images have been ascribed to them. 



It is of [tractical importance to be able to locate an injury to the visual 



