218 ELEMENTS OF ORNITHOLOGY. 
This organ consists of a main part called the cerebrum, formed 
of two lateral rounded masses placed side by side called the cerebral 
hemispheres, and which are medianly united to a certain extent. 
Immediately behind them is a single, transversely marked body 

Dorsau Aspect or BRAIN oF A PIGEON. 
2, One of the cerebral hemispheres; 3, pineal gland; 4, one of the optic 
lobes; 5, cerebellum. 
called the cerebellum, which if cut through shows a peculiarly 
ramified disposition of a darker and a lighter substance, 
termed the arbor vite. On each side of the hinder part of the 
cerebrum is a rounded body, and these two are called the optic 
Fig. 168. 

LeErt-sIDE VIEW OF BRAIN OF PIGEON. 
1, Olfactory lobe ; 2, left cerebral hemisphere; 3, pineal gland; 4, one of 
the optic lobes; 5, cerebellum ; 6, pituitary body ; 8, optic nerve. 
lobes, which lie rather beneath the front part of the cerebellum. 
The common base of the brain continues backwards in the 
median line, and is called the medulla oblongata, whichis directly 
continuous with the spinal cord. From the front end of each 
