52 BRAIN 
the corpora bigemina of Mammals, and the optic thalami; the 
dorsal roof forms the epiphysis or pineal gland, the corpus callosum 
and the anterior commissure, both of which consist of bundles of 
white nerve fibres and connect the right with the left hemisphere. 
The ventral portion of the hemispheres consists of the corpora 
striata, which are masses of grey brain-substance, and of the olfactory 
lobes, which mark the anterior end of the brain. 
The central canal, which runs through the spinal cord, is con- 
tinued into the brain, and forms the fourth ventricle in the hind- 
brain, extending dorsally into the cerebellum ; and is then continued 
as “aqueductus Sylvii” through the midbrain, with lateral exten- 
sions into the optic lobes. The dilatation of this canal in the 
thalamencephalon is the third ventricle: it extends ventrally 
towards the hypophysis as the infundibulum, in a similar way 
VERTICAL SECTION IN THE 
hem, pn MIDDLE LINE THROUGH 
THE BRAIN OF A DUCK. 
Enlarged. (After H. 
F. Osborne.) 
T, Right olfactory nerve ; 
IT, Right optie nerve and 
chiasma; acm, Anterior 
commissure ; cal, Corpus 
callosum ; cereb, Cerebel- 
tum; /t, Lamina termin- 
alis; fm, Foramen Mon- 
roi; hem, Right hemi- 
sphere; hph, Hypophysis ; 
inf, Infundibulum ; pem, 
Posterior commissure ; 
pn, Epiphysis or pineal 
gland, 
dorsally towards the epiphysis, and communicates through the 
foramen of Monro with the second and first ventricles ; these being 
the cavities of the two hemispheres. 
The hypophysis cerebri or pituitary body is lodged in the 
“sella turcica,” a niche or recess formed by the anterior and 
posterior basisphenoid bones. This peculiar body is probably the 
degenerated remnant of a special sense-organ in the mouth of early 
Vertebrata, it being developed partly as an outgrowth from the 
roof of the mouth which fuses with a corresponding growth from 
the brain and then loses its connexion with the mouth. 
The epiphysis cerebri or pineal body is the remnant of a 
sense-organ, possibly visual, as it is still functional in many Lizards 
possessing a lens, a retina-like accumulation of black pigment and 
a nerve, but quite degenerated in all Birds and Mammals. 
The cerebellum of Birds is homologous only with the “worm” 
or middle portion of the cerebellum of Mammals, the lateral lobes 
being absent, although a pair of flocculi are present. Externally 
it exhibits a number of transverse furrows, which divide it into 
