THE NERVOUS SYSTEM AND ORGANS OF SENSE. 219 
cerebral hemisphere a process proceeds forwards. These are 
the olfactory lobes. Between the cerebral hemispheres and the 
cerebellum, on the dorsal aspect of the brain, is a small process 
called the pineal gland. A median inferior prominence is called 
the pituitary body. Within, the brain is hollow, but the hollow 
space is variously disposed in different regions, and its walls are 
of very different thicknesses in different parts. Those parts of 
the cavity which extend into the hemispheres are called the 
lateral ventricles, and they open posteriorly by an aperture 
termed the foramen of Munro into a median cavity called the 
third ventricle. This is continued backwards into another beneath 
the cerebellum, which is the fourth ventricle. 
The spinal cord shows two enlargements where it gives off 
nerves for the wings and legs respectively. The posterior of 
these enlargements also contains a cavity or ventricle termed the 
sinus rhomboidalis. 
Some of the nerves given off from the brain go to the organs 
of sense, while others go to muscles and viscera. The points 
of exit from the skull of some of the nerves have been already 
indicated *. 
The Nose.—This consists of two nostrils, which open externally 
in the way before described t and which pass back to open 
internally on the roof of the mouth, generally by a single aper- 
ture there. The olfactory lobe (often called olfactory nerve) 
above mentioned supplies the nerves which give the power of 
smell, and they ramify on the membrane which lines the nasal 
cavities. 
The Organ of Taste—The tongue, which has been already 
described }, is a part which in other animals serves for gusta- 
tion, but probably has little or no power of taste in very many 
Birds. That sense is probably ministered to by the lining of 
the beak, which is doubtless also a most important instrument 
for ministering to the sense of touch. 
The Eav.—There is hardly any external ear, save sometimes a 
circle of feathers—as in the Bustard, Ostrich, and Owl. In the 
last-named bird the external opening is wide, and is protected 
by a flap of skin with a few folds, thus distantly resembling the 
human ear. The external opening leads into a very shallow 
cavity bounded by the quadrate, squamosal, and exoccipital bones, 
* See ante, p. 183. t See ante, p. 146. 
t See ante, p. 207. 
