AVE S. 



BRAIN. In birds the hemispheres of the brain assume a larger size in proportion 

 to the body than in the preceding classes. The surface of the brain is smooth and 

 without convolutions ; it contains two lateral ventricles, having very thin posterior 

 parietes, and separated from each other by the radiated septum ; each contains a very 

 large striated body which projects into it and occupies the greater proportion of its 

 space. Underneath the floor of the ventricles are the thalami, and between these the 

 third ventricle, which extends posteriorly into the optic lobes and into and underneath 

 the cerebellum to the calamus scriptorius. Two cords, the crura of the brain, proceed 

 from the hemispheres anteriorly, and pass just above the optic tracts to the oblong 

 medulla. There is an anterior, posterior, and soft commissure. Behind the thalami 

 are situated two rounded and rather flattened bodies, the optic lobes, which contain 

 ventricles ; behind these the cerebellum is situated, it is formed of a large convoluted 

 middle lobe with a lobule extending from each side, it is connected with a pedicle on 

 each side to the oblong medulla, it contains at its inferior part a ventricle, which 

 communicates with that leading from the third and optic lobes to the calamus 

 scriptorius. At the base of the brain the prominence is seen in the situation of the 

 mammillary eminences, and behind these the oblong medulla much larger than the 

 spinal cord. 



CEREBRAL NERVES. The olfactory nerve proceeds from the anterior lobe 

 of the brain, it spreads round the superior part of the Schneiderian membrane, and thus 

 forms an appearance of a hollow ganglion before its termination. The optic nerve 



