chap, xii.] BRAIN OF BIRDS. 423 



is not always a narrow plate, and in the Crocodilia 

 the central portion forms a distinct " vermis." 



Of the thickenings of the cerebral walls, the two 

 most important are the corpora striata in the 

 hemispheres, and the restiform bodies in the 

 medulla oblongata ; the former are the ganglionic 

 masses which become developed on the floor of the 



01 



Fig. 182 A. Lateral view of the Brain of Eabbit, to show the large 

 olfactory lobes, and the termination of the hemispheres in front of 

 the Cerebellum. (After Huxley.) 



A, Frontal lobes ; B, occipital lobes ; sy, sylvian fissure. 



brain, and, as they extend inwards, they encroach on 

 the cavity of the lateral ventricle ; as may be sup- 

 posed, they are largest in the Crocodilia. The cor- 

 pora restiformia in a similar manner encroach on 

 the fourth ventricle. 



In Birds the cerebral hemispheres are propor- 

 tionately still larger in size, and, as the optic lobes, 

 or so-called corpora bigemina (Fig. 181 (B) ; MH) are 

 now it at the sides and base of the brain, the 

 cerebral hemispheres so overlap them as to hide 

 them when looked for from above. The cerebellum 

 (Fig. 181 (B) ; HH) is much larger, and its lateral lobes, 

 or flocculi, may be distinguished from its central 

 body, or vermis; while in section this division of 

 the brain presents just the same appearance as the 



