570 



THE ORGANS 



(Fig. 376, Tro) terminate in the thalamus, in the lateral geniculate 

 body, and in the anterior corpus quadrigeminum (Fig. 376). 



Neurone System No. III. — The neurones of this system have 

 their cell bodies in the thalamus, lateral geniculate body, and anterior 

 corpus quadrigeminum (Fig. 376). The axones of the two former 

 terminate in the cortical visual centers in the occipital lobe (Fig. 376, 

 Co). The axones of the latter form descending reflex paths (see 

 Anterior Corpora Quadrigemina, p. 528). 



Neurone system No. I is the analog of the primary afferent neu- 

 Ij f. a, rones (the cerebro-spinal ganglion 



cells). Neurone system No. II is 

 the analog of the secondary afferent 

 neurone system which receives the 

 afferent root fibres and originates 

 the secondary decussating tracts 



Fig. 378 Fig. 379. 



Fig. 378. — From Longitudinal Section through Margin of Crystalline Lens, showing 

 longitudinal sections of lens fibres and transition from epithelium of capsule to lens 

 fibres. (Merkel-Henle.) a, Lens fibres; b, capsule; c, epithelium. 



Fig. 379. — -From Cross Section of Crystalline Lens, showing transverse sections of 

 lens fibres and surface epithelium. (Merkel-Henle.) a, Lens fibres; h, epithelium. 



to the thalamus, such as the medial and lateral fillets. Neu- 

 rone system No. Ill is the tertiary aft'erent neurone system or 

 thalamo-cortical system. It will thus be seen that the optic chiasma 

 is the analog of the decussations of the medial and lateral fillets. 

 (See also pp. 481, 482 A.) 



The Lens.^ — The lens is composed of lens fibres which are laid 

 down in layers (Fig. 378, a). The lens fibre is a long hexagonal, flat- 

 tened prism with serrated edges. Most of the lens fibres are nucle- 



