CHORDATA 



349 



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 350, and verify the statements there. 



3. Thickenings or thinnings of the roof, sides, or floor 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 teacher may, if he desire, pursue 

 the details somewhat further. 



FIG. 173. 



mcd. 



FIG. 173, Diagram of head and brain of human foetus 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 (A), cer, cerebellum; med, medulla oblongata; mes, mesencephalon; p, pituitary 

 body; pr, prosencephalon; s.c., spinal cord; th, thalamencephalon; i, olfactory nerve; a, 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 do not give the exact proportions between 

 the various parts of the vertebrate brain. The student is 

 urged to examine figures less diagrammatic in their nature in 

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



