76 



FREDERICK TILNEY AND LUTHER F. WARREN 



however, that the structure can be found in human embryos, though 

 in a rudimentary and inconstant condition. 



The so-called postvelar tubules or diverticula can be clearly fol- 

 lowed in every degree of complexity in embryos of 19 mm. up to 44 

 mm. and appear in every specimen studied in those stages. They 



24 



2 4 38 



42 



40 33 32 



Fig. 42 Mesial view of forebrain reconstruction of 70 mm. cat embryo. X 25. 

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

 Tilney, 1915. 



2, chiasmatic process; 4, chiasm; 5, corpus interpedunculare; 7, epip.hysis; 9, 

 foramen of Monro; 13, infundibular process; 24, midbrain; 27, mammillary body; 

 32, post-chiasmatic eminence; 33, post-chiasmatic recess; 34, post-infundibular 

 eminence; 35, post-infundibular recess; 38, pre-chiasmatic recess; 40, recess of 

 infundibular process; 41, supra-optic crest; 42, supra-optic recess. 



begin at the diencephalic lip of the velum, have definite limits and 

 involve a relatively short extent of the oral end of the diencephalic 

 roof-plate. They always appear as outgrowths from the brain roof 

 and are to be distinguished from ingrowths due to plexus formation. 



Warren's 417 description of the conditions in the sheep is as 

 follows : 



