THE CHICKEN. 



101 



a flying arch extending entirely to the sternum. The 

 posterior limbs are made up of a short, strong thigh, a 

 leg, and a tarsus, corresponding at the same time to the 

 tarsus and metatarsus, and digits ordinarily four in num- 

 ber. The much-elongated metatarsus constitutes what is 

 ordinarily called the leg of the fowl. The number of 

 phalanges follows a rule that is constant for birds. The 

 first digit has two phalanges, the second has three, the 

 third four, and the fourth five. Besides these, the cock 

 has a spur, which is a sort of bony prolongation of the 

 metatarsus, and must not be mistaken for a digit. 



The nervous system comprises the same parts as in 

 the dog, but these are modified to some extent. The 

 convolutions of the cerebrum are almost wanting ; the 

 cerebellum, instead of being formed of largely-developed 

 lateral lobes with a thin median 

 lobe, has a large median lobe 

 and very small lateral lobes. 

 Lastly, there is no corpus cal- 

 losum. 



The organs of sense are for 

 the most part well developed. 

 However, the tongue is re- 

 duced to a pointed, horny, and 

 very thin appendage ; this leads 

 us to the conclusion that the 

 sense of taste is very feeble. 



The eye is very large in pro- 

 portion to the size of the head, and is in all birds pro- 

 tected by three eyelids, two horizontal and one vertical ; 

 the latter comes from the internal angle of the eye, and 

 is called the nictating membrane. The iris is large and 

 pierced by a round pupil. A black membrane, folded 



FIG. 55. 



EYE OF BIRD. 



