524 



ZOOLOGY. 



free barbs, called plumules. Over the tail-bone (coccyx) 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- m , , . . , -, 



him; d', its lateral parts ; e, medulla. -After 1 he brain IS much larger 



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 oesophagus 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 proventriculus, 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 



Fig. 458. Thymus (th) and thyroid (0 

 glands of a young hawk, Buteo vulgaris 



. ...... -i ..-. KiauuD vi a pining iiavviv, jjuieu pwww^a 



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



a firm horny layer, by which 



the food is crashed and comminuted, thus taking the place 



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



