403 



# 



^ I M 



* 



Fig. 272. — Pineal Gland of a Man aged 40, showing Astrocyte Cells 

 and Neuroglial Fibres. (After R. Amprino.) 



or in other words, furnishing the means by which osmotic processes can 

 take place between the cells and the tissue-fluid. 



The Nerves of the Parietal Organ and Pineal Body 



The study of the nerve supply of the human pineal organ necessarily 

 involves a preliminary consideration of the pineal nerves, commissural 

 fibres, and the associated ganglia of lower types of animals in which the 

 parietal sense-organs, pineal sac, and pineal stalk are more highly evolved 

 than they are in mammals, and in which the nerve tracts have been 

 definitely traced from their origin in the sensory-cells of the retina of 

 the pineal eye or the wall of the pineal sac to their termination in the nerve 

 tracts and ganglia of the brain. 



A feature of special interest in connection with the nerve supply of 

 the pineal eye is the bearing that this has upon the question of the bilateral 

 original of the pineal system, and the closely related problem of the 

 homology of the pineal organ of birds and mammals with reference to 

 the " parapineal organ " of cyclostomes and the pineal sac and pineal 

 stalk of amphibia and reptiles. The nerve supply of the pineal eye and 

 pineal sac in Sphenodon was specially studied with reference to this 

 question by the late Professor A. Dendy (191 1, Phil. Trans. Roy. Soc, 

 Ser. B., Vol. 201, pp. 228-339) (Figs. 183, 184, 185, A, Chap. 20, pp. 259, 

 260, 261). Unfortunately this important work appears to have escaped 

 the attention of many modern writers on this subject, owing to the cir- 



