3SO 



ZOOLOGY 



Questions on the figures. — What portions of the adult brain are produced 

 from each of the three primary lobes? Where are the principal outgrowths, 

 thickenings and thin portions of the wall? In comparison with figure D what 

 portions of the brain become highly developed in the higher Vertebrates? Make 

 a diagram based on D, which will show the general relation of these parts in man. 

 Compare the diagrams with the table on page 349, and verify the statements there. 



3. Thickenings or thinnings of the roof, sides, or fioor of 

 the tube may produce lobes and affect the size of the cavity of 

 the tube. The accompanying diagrams and table will furnish 

 an outline from which the student may pursue the details some- 

 what further. 



Fig. 173. 



Fig. 173. Diagram ot bead and brain of human fcetus six weeks old (heavy boundaries). The 

 dotted line indicates the outline of the brain of a foetus three months old. Note the great growth 

 of the hemisphere (/t). £er, cerebellum; med^ medulla oblongata; mes, mesencephalon; p. pituitary 

 body; pr, prosencephalon; s.c.^ spinal cord; th^ thalamencephalon; i. olfactdry nerve; 2, optic nerve. 

 Compare with Fig. 172. 



Questions on the figure. — Locate point by point the corresponding regions in 

 the diagrams in Fig. 172. What are the chief points of modification? Note par- 

 ticularly the great flexures of the organ. Where is the cerebellum of the older 

 embryo? What is the nature of the pituitary body in the adult? 



These diagrams (Fig. 172) do not give the exact proportions 

 between the various parts of the vertebrate brain. The student 

 is urged to examine figdres less diagrammatic in their nature in 

 the larger texts. See, Fig. 173; also, Edinger: "Anatomy of 



