NERVOUS SYSTEM. 



605 



The hind-limb consists of a short stout femur, a tibia to 

 which the proximal tarsals (astragalus and os calcis) are 

 fused (forming a tibio-tarsus), an incomplete fibula joined 

 to the tibia, three metatarsals fused to one another and to 

 the distal tarsals (forming the tarso-metatarsus), a free first 

 metatarsal, and, finally, the four toes. The 

 first, turned backwards, has two phalanges, 

 the second three, the third four, and the 

 fourth five. 



Nervous system. — In contrast to the brain 

 of crocodiles and other Reptiles, the brain 

 of the pigeon and other Birds fills the 

 cranial cavity. The cerebral hemispheres 

 are large and smooth. Their roof is thin, 

 their main mass consists of the large cor- 

 pora striata which bulge into the ventricles. 

 They meet the cerebellum and throw the 

 solid optic lobes to the sides. The olfactory 

 lobes are very small (cf. deficient sense of 

 smell). Between the cerebral hemispheres 

 and the cerebellum, the pineal body rises 

 to the surface, and a slight posterior separa- 

 tion of the hemispheres will disclose the 

 region of the optic thalami. The cerebellum 

 is ridged transversely and divided into a , 

 median lobe and two small lateral flocculi. r 

 The curvature of the brain is well marked in 

 the adult, thus the medulla is quite hidden 

 by, and descends almost vertically from, F,G ; r^s—Bones 



V , ,, of hind-limb of 



the cerebellum. 



eagle. 



J., Femur; t.t., 

 tibio-tarsus ; /l>., 

 fibula ; «., ankle- 

 joint ; mt., tarso- 

 metatarsus; mf., 

 first metatarsal 

 (free). 



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. 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 



