542 C. JUDSON HEPKICK 



EXPLANATION OF FIGURES 



71. Diagrammatic cross section through the brain of young Echidna, after 

 Eiliot Smith, '03, p. 468, fig. 16. 



a, dorsal part of the paraterminal body. 

 /3, sulcus limitans hippocampi 



7, ventral part of the paraterminal body. 



8, fissura hippocampi. 



72. Diagrammatic median section of the brain of a hypothetical vertebrate 

 ancestor, showing the probable relations of the rostral end of the neural tube be- 

 fore the evagination of the optic vesicles and cerebral hemispheies. The site of 

 the tissue which gives rise to the optic vesicle is shown at R, to the olfactory bull) 

 at 0. (See the text, pp. 468, ff.) 



