264 THE PINEAL ORGAN 



First, the primary position of the nerve-fibres in the outermost zone of 

 the wall of the pineal sac recalls the conditions found by Braem and 

 Studnicka in Rana temporaria. In Rana the nerve-fibres commence 

 deeply in the wall of the distal part of the pineal organ, but as they approach 

 the stalk they converge and form a definite tract, which lies upon its dorsal 



^,-par.o. 



p.int 



jV^t.— *tapi. 



B 



Fig. 187. 



A — The parietal region of a 26-mm. embryo of Anguis fragilis, showing the 

 position of the parietal nerve in front of the epiphysis and passing towards 

 the habenular commissure. Diagram constructed from three sections. 

 (After Beraneck.) 



B — The proximal part of the epiphysis from an 18-day embryo of Iguana tuber- 

 culata, showing the position of the pineal tract, which, emerging from the 

 posterior wall of the epiphysis, passes to the posterior commissure. (After 

 Klinckostroem .) 



c. hab. : habenular commissure. 



c.p. : posterior commissure. 



d.s. : dorsal sac. 



Ep. : epiphysis. 



n. par. : nervus parietalis. 



p. int. : pars intercalaris. 

 par. : paraphysis. 

 par. o. : parietal organ. 

 tr. pi. : tractus pinealis. 

 v. : velum 



aspect and finally leaves this to join the posterior commissure (Fig. 166, 

 p. 232); while in Iguana tuberculata (Fig. 187), as shown by Klinckow- 

 stroem, the nerve quits the posterior wall of the pineal organ high up and 

 runs an independent course through the connective tissue to the posterior 

 commissure. Although a striking contrast is afforded between these 

 cases and those in which the nerve-fibres pass to the posterior commissure 



