524 



ZOOLOGY. 



free barbs, called plumules. Over the tail-bone (coccytf are 

 usually sebaceous glands, which secrete an oil, used by the 



bird in oiling and dress- 

 ing or "preening" its 

 feathers. In some birds, 

 especially in the males of 

 the gallinaceous fowls, as 

 the cock and turkey, the 

 head and neck are orna- 

 mented with naked folds 

 of the skin called " combs" 



Fig. 457. Brain of the Hen. A , from above, ,, 



B, from below ; a, olfactory bulbs ; b, cere- and wattles, 

 bral hemispheres ; c, optic lobes ; d, cerebel- mi .... 

 lum ; d', its lateral parts ; e, medulla. After lllC braill IS mucll larger 



Cams, from Gegenbaur. ,-, xl ,.-, ,-. 



than in the reptiles, the 



cerebral hemispheres being greatly increased in size, while 

 the cerebellum is transversely furrowed, and is so large as to 

 cover the whole of the me- 

 dulla. The alimentary tract 

 consists of an O3sophagus as 

 long as the neck ; it dilates 

 in the domestic fowl and other 

 seed-eating birds, as well as 

 in the raptorial birds, into a 

 lateral sac called the crop (in- 

 gluvies). The stomach is di- 

 vided into two parts, the first, 

 the proventricultte, which is 

 glandular, secreting a digest- 

 ive fluid ; and the second, 

 which corresponds to the pylo- 

 ri c end of the stomach in the 

 mammals, is round, with mus- 

 cular walls, especially develop- 

 ed in seed-eating birds, and 

 called the "gizzard." In the 



i .-, . -, . -.. j .,- glands of a young hawk, Buteo milgaris 



fowl the gizzard IS lined With of Europe ; tr, trachea.-After Gegen- 



a firm horny layer, by which * 



the food is crushed and comminuted, thus taking the place 



of teeth. The intestine (including the large and small intes- 



Fig. 458. Thymus (th) and thyroid (f) 



