THE BIRDS 209 
sionally veering in to get their bearings or to rest, espe- 
cially in the presence of fogs. 
195. Classification.—Most zoologists make two primary 
divisions of the living types of birds—those like the ostrich 
with flat breast-bones, and the other the ordinary birds, in 
which the breast-bone has a strong keel for the attachment 
of the powerful muscles used in flight. This distinction is 
not of high importance, but we may use it as a convenience 
in the description of a few typical forms belonging to sev- 
eral orders into which these two divisions are subdivided. 
196. The ostriches, etc. (Ratite)—From specimens in- 
troduced or from pictures we are doubtless familiar with 
the ostriches and with some of their relatives. The African 
ostrich (Struthio camelus, Fig. 121) is the largest of living 
birds, attaining a height of over seven feet, and is further 
characterized by a naked head and neck, two toes, and 
fluffy, plume-like feathers over parts of the body. They 
are natives of the plains and deserts of Africa, where they 
travel in companies, several hens accompanying the male. 
When alarmed, they usually escape by running with a swift- 
ness greater than that of the horse, but if cornered they 
defend themselves with great vigor by means of their 
powerful legs and beaks. Their food consists of insects, 
leaves, and grass, to which is added sand and stones for 
grinding the food, as in the domestic fowl. The American 
ostriches or rheas, are smaller ostrich-like birds, living on 
the plains of South America. Their habits are essentially 
the same as those of the African species. ; 
197. The loons, grebes, and auks (Pygopodes).—The birds 
in this and some of the following orders are aquatic in 
their habits. All have broad, boat-like bodies, which, with 
the thick covering of oily feathers, enables them to float 
without effort. The legs are usually placed far back on 
the body—a most favorable place for swimming, but it ren- 
ders such birds extremely awkward on land. The grebes 
are preeminently water-birds. The pied-billed grebe or dab- 
