44 FKEDERICK TILNEY AND LUTHER F. WARREN 



time before the appearance of the paraphysis. In the embryo 

 of an !! mm. Mustelus the evagination appears rising well 

 above the general plane of the roof. 



It is bounded by a thin cephalic and a thicker caudal wall. 

 A recess of considerable depth extends into it; it retains com- 



44 



29 



Fig. 11 Mesial view of forebrain reconstruction of 11 mm. Mustelus embryo. 

 X 100. The unshaded area shows the cut surfaces of the reconstruction. Ac- 

 cording to Tilney, 1915. 



4, chiasm; 7, epiphysis; 18, infundibular evagination; 24, midbrain; 25, mam- 

 millary region; 29, optic evagination; 36, post-infundibular evagination; 44, tel- 

 encephalon; 45, tuberculum postero-superius; 46, tubercle of the floor of Schulte. 



munication with the third ventricle. The inception of the velum 

 transversum may be discerned, but no paraphysis is present. 

 The changes observed in passing from the 11 mm. to the 20 mm. 

 embryo consist in the now definite appearance of the velum 

 transversum and the elongation of the pineal organ. 



