THE PINEAL SYSTEM OF REPTILES 



243 



nerve, the nervus parietalis, not connected to the epiphysis, but joining 

 the habenular commissure ; (b) a posterior part, the epiphysis — Hoff- 

 mann, Lacerta agilis (1886) ; Strahl and Martin, Anguis, L. vivipara 

 (1886). 



(4) A single diverticulum, the distal part of which becomes divided by 

 an incomplete transverse septum into an anterior and posterior part, in 

 such a way that the lumina of the two end vesicles communicate with the 

 lumen of a common stalk — Beraneck, Lacerta (1894). 



Fig. 172, D. — Sagittal Section through the Pineal Organ of an Embryo 



of Lacerta vivipara, 9 mm. (After Nowikoff.) 

 The nerve-fibres were traced through the habenular commissure into the right 

 habenular ganglion. According to Graham Kerr, they are formed at the time 

 when the vesicle is in contact with the roof of the thalamencephalon and 

 afterwards elongate as the vesicle becomes gradually separated from the 

 brain (see Fig. 173). 



/. : lens; pn. : parietal nerve; p.s. : pineal stalk and pineal sac; 

 ret. : retina ; thai. : roof of thalamencephalon. 



(5) The parietal eye arises not as an independent structure but as an 

 outgrowth from the anterior wall of the primary diverticulum — Klinckow- 

 stroem, Iguana (1894) '■> McKay, Grammatophora muricata (1888) ; and 

 Schauinsland, Sphenodon (1899). 



(6) Two completely independent outgrowths soon unite with each 

 other — Francotte, L. vivipara (1894). 



(7) The rudiments of two pairs of serially arranged sense organs 

 become fused in the median plane, the anterior giving rise to the parietal 

 organ, the posterior to the epiphysis, and when present an accessory 

 parietal or pineal organ. 



