THE PINEAL BODY 



75 



The primary arches can be demonstrated in early human embryos 

 from 10 to 15 mm. in length. 



Of the embryos of 15 mm. and over examined there were about thirty 

 in which the brain was in suitable condition to warrant making obser- 

 vations, and in addition to these a number of others were studied but 

 excluded on account of injury or distortion of the forebrain. In the 

 thirty specimens only eight showed any possible signs of a paraphysis 

 and most of these were mostly rudimentary in character. By counting 

 every possible case we get a result of 27 per cent. The fact remains, 



-20 



27 



Fig. 41 Mesial view of forebrain reconstruction of 51 mm. cat embryo X 50. 

 The unshaded area shows the cut surfaces of the reconstruction, according to 

 Tilney, 1915. 



2, chiasmatic process; 4, chiasm; 5, corpus interpeduncularo; 7, epiphysis; 9, 

 foramen of Monro; 11, infundibular stem; 13. infundibular process; 20, lamina 

 terminalis; 27, mammillary body; 32, post-chiasmatic eminence; 33, post-chias- 

 inatic recess; 35, post-infundibular recess; 36, post-infundibular evagination; 39, 

 dorsal sac; 40, recess of the infundibular process; 42. supra-optic reces'. 



