6o6 



BIRDS. 



an incomplete fibula joined to the tibia, three metatarsals 

 fused to one another and to the distal tarsals (forming the 

 tarso-metatarsus), and, finally, three 

 toes, of which the innermost has two 

 phalanges, the next three, and the 

 outermost four. 



ft 



Nervous System. 



In contrast to the brain of croco- 

 diles 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 corpora 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. Between the cerebral 

 hemispheres and the cerebellum, 

 the pineal body rises to the surface, 

 and a slight posterior separation of 

 the hemispheres will disclose the 

 region of the optic thalami. The 

 cerebellum is ridged transversely 

 and divided into a median and two 

 lateral regions. The curvature of 

 the brain is now 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 fore-arm, 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 the pia 

 mater. The cervical part of the sympathetic nervous system is double 

 on each side. 



FIG. 212. Bones of 

 hind leg of Eagle. 



/., Femur : tt., tibio-tarsus ; 

 /#., fibula ; ., ankle joint ; 

 mt., tarso-metatarsus ; mP. t 

 ist metatarsal (free). 



