746 



PHYLUM CHORDATA : CLASS AVES — BIRDS 



ridged transversely and divided into a median lobe and 

 two small lateral flocculi. The curvature of the brain 

 is well marked in the adult ; thus the medulla is quite 

 hidden by, and descends almost vertically from, the 

 cerebellum. 



There are as usual twelve cranial nerves. 



In connection with the spinal cord, the brachial plexus of nerves 

 to the forearm, and the sacral plexus to the leg, should be noticed. 



OLF.L- 



AV'O. 



Fig. 447- — Brain of pigeon (I. dorsal, II. ventral, III. lateral aspects). 



OLF.L., Olfactory lobes ; C.H., cerebral hemispheres ; P.B., phieal body 

 or epiphysis; O.L., optic lobes; CB., cerebellum; FL., flocculus or 

 lateral extension of cerebellum ; M.O., medulla oblongata ; PIT., 

 pituitary body at end of infundibulum {INF.) ; O.N., optic nerves 

 crossing in the chiasma. 



In the lumbar region the halves of the cords diverge for a short 

 distance, forming a wide space— the rhomboidal sinus — roofed only 

 by membrane. The cervical part of the sympathetic nervous system 

 is double on each side. 



Sense organs. — The sense of smell is not well developed 

 in Birds. The nostrils are longitudinal slits overhung by 

 the swollen, more or less tactile, cere. Apart from the 

 cere, there is only a diffuse sense of touch, and the sense 

 of taste is also slightly developed. 



The sense of hearing is acute. Externally the ear is 



