46 



FREDERICK TILNEY AND LUTHER F, WARREN 



has not yet made its appearance. In the 50 mm. embryo, how- 

 ever, the paraphyseal anlage is present and the pineal organ 

 has become still further elongated. 



The tendency toward expansion of the dista 1 extremity is not 

 as marked as in the 20 mm. embryo. The pineal organ still 

 contains a lumen throughout its entire extent. The expansion 

 of the pineal organ to form an end-sac is again pronounced at 

 the stage of 70 mm. 



44 



39 



32 



13 



Fig. 13 Mesial view of forebrain reconstruction of 50 mm. Mustelus. X 50. 

 The unshaded area shows the cut surfaces of the reconstruction. According to 

 Tilney, 1915. 



2, chiasmatic process; 3, cerebellum; 4, chiasm; 7, epiphysis; 13, infundibular 

 process; 24, midbrain; 25, mammillary region; 32, post-chiasmatic eminence 

 (lobus-inf erior) ; 33, post-chiasmatic recess (recess of inferior lobe); 36, post- 

 infundibular evagination; 39, paraphysis; 40, recess of infundibular process; 41, 

 supra-optic crest ; 42, supra-optic recess ; 44, telencephalon ; 47, velum transversum . 



