664 BIRDS. 
the tibia, three metatarsals fused to one another and to 
the distal tarsals (forming the tarso-metatarsus), a free first 
metatarsal, and, finally, the four toes. The first, turned 
backwards, has two phalanges, the second three, the third 
four, and the fourth five. 
Nervous system.—In contrast to the brain of crocodiles 
and other Reptiles, the brain of the pigeon and other 
Birds fills the cranial cavity. The cerebral hemispheres 
Fic. 368.—Brain of pigeon (I. dorsal, II. ventral, III. lateral aspects). 
OLF.L., Olfactory lobes ; C.H., cerebral hemispheres; PB., pineal body ; 
OL., optic lobes; CB., cerebellum; FZ., flocculus or lateral exten- 
sion of cerebellum; 47.0., medulla oblongata; P/7., pituitary body 
at end of infundibulum (/VF.); O.V., optic nerves crossing in. the 
chiasma. 
are large and smooth. Their roof is thin, their main mass 
consists of the large corpora striata which bulge into the 
ventricles. They meet the cerebellum and throw the solid 
optic lobes to the sides. The olfactory’ lobes are very 
small (cf. deficient sense of smell). Between the cerebral 
hemispheres and the cerebellum, the pineal body rises to 
the surface, and a slight posterior separation of the 
hemispheres will disclose the region of the optic thalami. 
The large cerebellum is ridged transversely and divided 
into a median lobe and two small lateral flocculi. The 
