38 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS 



brain (No. 3), the cerebellum (cb) from the hindbrain 

 (No. 1), and from the midbrain (No. 2) the formation 



Fig. 24. 



or outgrowth of the swellings characteristic of the optic 

 lobes (Fig. 23). The next step is that the outgrowths 

 from 1 and 3 — i. e., the cerebellum and cerebrum — in- 

 crease enormously. This is especially true of the cere- 

 brum, which, commencing as the foremost in the series, 

 grows forward, sidewise, and especially backward, cov- 

 ering first the thalamus (Fig. 24), then the optic lobes 

 (Fig. 25), and finally the cerebellum, and thus masks the 



Fig. 25. 



true structure of the brain (Fig. 26). The following 

 schedule gives the parts as brought out by embryology. 



