714 



A TEXTBOOK OF PHYSIOLOGY 



fourth, and sixth nuclei. The superior corpus quadrigeminuin is to 

 be regarded as the co-ordinating centre for eye movements. It 

 is ultimately related with the chief centre of co-ordination the 

 C3rebelliun. 



In mammals, the development of the optic connections is measured 

 by the importance of vision to the animal. The squirrel requires 

 accurate vision, and has large optic nerves and well -developed anterior 

 corpora quadrigemina. In the rabbit and the hare, a wide panoramic 

 vision, together with an acute sense of hearing, is necessary to escape 

 capture. The eyes are placed laterally, and the fibres of the optic 

 nerve cross almost completely. 



Synia 



sept, lucid.. 



striae longitud. 

 gyrus subcallos 



supra-cal/osal 

 gyms 



tract (B) 



mesial root 

 anterior perforated space 



'uncus ^collateral fissure 



band of Giacomini 

 uncus 

 temp, incis. 



FIG. 437. SHOWING CONNECTION OF THE RHIKBNCBPHALON (OLFACTORY BULB) 



WITH THE HlPPOCAMPAL CYRUS AND THE UNCUS. (Keith.) 



In birds, the optic chiasma is single and complete. The fibres 

 from each nerve interlace and alternate, but eventually all pass to the 

 opposite side around the optic thalami to well-developed geriiculate 

 bodies. The optic lobes are well marked in birds of prey. Vision is 

 as a rule panoramic, one eye for each side. In owls and hawks, 

 which possess a considerable amount of binocular vision, it is probable 

 that all the fibres decussate, so that the vision, although being binocular, 

 is not stereoscopic. In fishes, the optic nerves cross completely, and 

 pass to the opposite optic lobe. 



The effect of injury to the visual tract in man differs according to the 

 site of the lesion. Section of the optic nerve causes total blindness in 

 the corresponding eye. A median section of the optic chiasma brings 

 about blindness in the nasal halves of both retinae, inducing a hemi- 

 anopia in the outer fields of vision of both eyes. Section of the optic 



