70 



FREDERICK TILNEY AND LUTHER F. WARREN 



At this time the pineal region presents a well-marked para- 

 physis, a velum transversum, and a dorsal sac. At the stage of 

 eight days in the chick a marked change is noticed, for at this 

 period of development the pineal anlage has the appearance of a 

 wide and expansive evagination in free communication with the 

 third ventricle. 



Fig 37 Mesial view of forebrain reconstruction of chick of 8 days 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; 9, foramen of 

 Monro; 11, infundibular stem; 12, infundibular canal; 13, infundibular process; 

 24, midbrain; 25, mammillary region; 26, mammillary recess; 32, post-chiasmatic 

 eminence; 35, post-infundibular recess; 36, post-infundibular eminence; 38, pre- 

 chiasmatic recess; 39, paraphysis; 41, supra-optic crest; 42, supra-optic recess; 

 44, telencephalon. 



The brain of the chick at fourteen days and eighteen hours 

 shows a marked alteration in the pineal region, as a result of 

 which the development of the epiphysis seems to overshadow all 

 other structures in this region. The walls of the evagination 

 which characterize the pineal organ in the eight-day chick have 

 become greatly thickened near the distal extremity of the epi- 

 physis so that now this portion of the organ is practically solid 



