168 



A MANUAL OF ANATOMY. 



large brains would be as 1 : 4, while among ignorant people 

 the ratio of large brains to the rest would be as I : 20. 



The Development of the Brain. In order to understand 

 the relations of the several parts of the brain to each other 

 it is very necessary that the changes which take place 

 during the process of development should be rehearsed. 

 The following is only the briefest summary of the import- 



Diag. n. A DIAGRAM OF THE 

 PRIMITIVE MEDULLARY GROOVE. (/. 

 S. H.) 



Diag. 12. THE PRIMITIVE ME- 

 DULLARY "TUBE" AND ITS DIVISIONS 

 INTO CEREBRAL VESICLES. (/. S. 

 H.) x, The lamina terminalis. 



ant changes ; many steps have to be omitted for lack of 

 space. The student is referred for a complete treatise on the 

 subject to Minot's " Embryology." 



The cerebrospinal system is developed from the epiblastic 

 (ectodermal) layer of the blastoderm, and its first appearance 

 is in the nature of a gutter along the blastoderm formed by 

 the heaping up of the cells. 



