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' 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. 



25 



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-inferior) ; 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 . 



