260 



THE PINEAL ORGAN 



plane. The nerve accompanied by the artery is enveloped for some 

 distance in folds of the pineal sac. Near the lower end of the sac its 

 histological structure undergoes an abrupt change, the small oval nuclei 





,pp- 



Fig. 184. — A, B, C. — Transverse Sections showing Some of the Relations 

 of the Nerve of the Pineal Eye (N. Parietalis), of an Adult Sphenodon. 

 The Sections Pass from before Backwards. (After Dendy, 191 i.) 



A — Nerve enclosed in capsule of eye. B — Nerve divided into two strands. 

 C — The subdivisions of the nerve have reunited to form a single nerve, 

 which lies above the distal end of the paraphysis. D — Transverse section 

 through the nerve of the pineal eye, showing its fibrous sheath, and nuclei 

 of the non-medullated fibres. These disappear in the proximal part of its 

 course. 



a.p.a. : anterior pineal artery. 



a.s. : saccular artery. 



c.e. : external capsule. 



c.f. : fibrous sheath. 



d.m.e., and d.m.i. : external and internal 

 layers of dura mater. 



n.p.e. : nerve of pineal eye. 



n.p.n. : nuclei of pineal nerve-fibres. 



par. : paraphysis. 



p.p. : parietal plug. 



r .a.p.a. : branch of anterior pineal 



artery. 

 r.b.p.a : recurrent branch of anterior 



pineal artery. 

 r.p.a. : anastomosing branch of pineal 



artery. 

 si. : superior longitudinal sinus. 

 so. c. : suboccipital cartilage. 



which are present in the course of the nerve-fibres throughout the first 

 part of its course cease and the single nerve breaks up into a number of 

 separate non-nucleated fibres, which spread out in the narrow interval 



