LECTURE II. 



EMBRYOLOGY AND COMPARATIVE ANATOMY OF THE BRAIN. 



GENTLEMEN: The hollow medullary tube of the vertebrate 

 embryo presents at a very early stage three vesicular enlarge- 

 ments at that end which later on develops into the brain. These 



Com m rss . post .. 

 GlonJ.pi*tal. 



ebellu.m, 



Htjpophijsen 



FIG. 4. 



Longitudinal section through the head of an embryo chick of 4J^ days. The five brain- 

 vesicles are pretty clearly marked. In the roof of the inter-brain is a fold which later 011 

 becomes the pineal gland. The epithelium of the pharynx is being pushed up toward 

 the base of the brain, and is the first rudiment of a portion of the hypophysis. (After 

 Mihalkovics.) 



HinterhirnhoJile, Hind-brain cavity. . NarhliirnhoMf, After-hrain cavity. 



ffypophysenunltige. Rudiment <>f hypophysis. Vtfi'hilti'l, Corpora quadrigemina. 



Jfvtelhirnh'dhle (aquoiduct), Mi'l-lmiin cavity. Vorrlrrhirnhohle, Fore-brain cavity. 



Zwiachenhimfiohle, Inter-brain cavity. 



are the (primitive) fore-brain, mid-brain, and hind-brain. The 

 latter is soon divided into two parts by the cerebellum growing 

 out of the anterior portion of its roof. These two divisions 

 eventually become the cerebellum and the medulla oblongata 

 (after-brain). 



The wall which closes the primary fore-brain in front is 

 called the "embryonic terminal lamina." From this there are 



(13) 



