406 THE PINEAL ORGAN 



The nerve-fibres of the functional lateral eyes in the human subject 

 are unmyelinated until a late period of foetal life, and do not become 

 myelinated until shortly before birth (Lucas Keene and Hewer, Lang- 

 worthy, O.R.). In the pineal eye of Geotria and Sphenodon the nerves 

 remain unmyelinated even in the adult animals, a condition which is to 

 be expected in organs which even in these species are degenerate and 

 apparently have little or no function. In other types, for instance in 

 many reptiles and amphibia, the pineal nerve or tract, though present 

 in early embryos (Fig. 187, Chap. 20, p. 264, and Fig. 273), usually 

 disappears later, when the terminal vesicle (parietal organ) becomes 

 separated from the pineal sac and its peduncle (Beraneck, E., p. 246 ; 

 Dendy, A., p. 261 ; Klinckowstrom, A. de, pp. 241, 243). 



The Nerve-fibres and Nerve Cells of the Mammalian Pineal Organ 



Both in the past and recently, and in addition to the work done on 

 the nerve supply of the pineal system in fishes, amphibia, and reptiles, 

 a large amount of work has been devoted to the study of the sensory cells, 

 nerve cells, and tracts of nerve-fibres belonging to the pineal system in 

 the human subject and in various types of mammals. This has been 

 carried out largely with the object of demonstrating an anatomical basis 

 by which it may be presumed the pineal organ or epiphysis is capable of 

 being influenced by afferent impulses and can function : either by means 

 of specific hormones secreted by the pineal cells and carried to distant 

 organs in the circulating blood or by means of efferent nerves issuing 

 from the gland and joining the habenular ganglia and other nerve centres 

 of the brain or the intracranial sympathetic system — exerting through 

 these systems a direct influence on other organs, e.g. the secretory cells 

 of the choroid plexuses, or an indirect influence on these cells, by means 

 of vasomotor nerves regulating the circulation of blood in the vessels of 

 the organs supplied by them. 



The anatomical demonstration of the distribution of the nerve-fibres 

 has been greatly facilitated by the various methods of silver impregnation, 

 and the definite results obtained by Retzius, Studnicka, Cajal, Pastori, 

 and other workers have done much to establish the existence and con- 

 nections of nerve-fibres, which are presumably afferent and efferent and 

 may form the basis of a reflex mechanism by which it is possible for the 

 pineal body to be influenced apart from the action of hormones reaching 

 it through the circulating blood. 



Theoretically one may postulate the existence of a pineal nerve supply 

 consisting of a double central and a double sympathetic system, thus : 



_ , fAfferent nerve-fibres to the pineal body. 



Central nervous system < „„, n , r , , 1 j 



[Efferent nerve-fibres from the pineal body. 



