132 ON THE DIGESTIVE FUNCTION, &c. 



quadrupeds ; for among- birds the ostrich has two ventricles,* and among 

 fishes the stomateus hiatola. The horse and ass, on the contrary, though 

 graminivorous quadrupeds like the ox, have only one stomach. 



There may seem, perhaps, something- playful in this application of different 

 systems of mechanism to the same class of animals, and of the same system 

 to different classes : but it shows us, at least, that the hand of nature is not 

 necessarily fettered by its own general laws, nor compelled, even under the 

 same circumstances, to adopt the same cause to produce the same effect. 

 Yet, if we had time, we might proceed beyond this remark, and point out, if 

 I mistake not, the reasons for such diversities, and the- skill with which they 

 are introduced. Thus the horse and ass are formed for activity, and require 

 lightness ; and hence the bulk and complexity of three or four stomachs would 

 counteract the object for which they are created; but it does not interfere with 

 the pursuits of the ox, which is heavy and indolent in its nature ; and which, 

 though it, may perhaps be employed as a beast of burden, can never be made 

 use of for speed. The activity of the horse and ass, moreover, excites, from 

 the stimulus it produces, a larger secretion of gastric juice than is met with in 

 the ox, and thus in a considerable degree supplies a substitute for the three 

 deficient stomachs ; but it by no means extracts the nutriment so entirely from 

 the food introduced into it ; and we hence see the reason why the dung of 

 horses is richer than that of black cattle, and why they require three or four 

 times as much provender. 



We may apply the whole of these remarks to the ostrich, whose peculiar 

 habitation is the sandy and burning deserts of the torrid zone, where not a 

 blade of grass is to be seen for hundreds of miles, and where the little food 

 it lights upon must be made the most of. The double stomach it possesses 

 enables it to accomplish this purpose, and to digest coarse grass, prickly shrubs, 

 and scattered pieces of leather, with equal ease. This animal is supposed to 

 be one of the most stupid in nature, and to have no discernment in the choice 

 of its food; for it swallows stone, glass, iron, and whatever else comes 

 in its way, along with its proper sustenance. But it is easy to redeem 

 the ostrich from such a reproach, at least in the instance before us ; for these 

 very articles, by their hard arid indestructible property, perform the office of 

 teeth in the animal's stomach ; they enable it to triturate its food most mi- 

 nutely, and to extract its last particle of nutriment. It is true that in the 

 class of birds, or that to which the ostrich belongs, a double stomach must 

 necessarily, to a certain extent, oppose the general levity by which this class 

 is usually characterized. But the wings of the ostrich are riot designed for 

 flight : they assist him in that rapidity of running for which he is so cele- 

 brated, and in which he exceeds all other animals, but are not designed to 

 lift him from the earth. In reality, the ostrich appears to be the connecting 

 link between birds and quadrupeds, and especially ruminant quadrupeds. In 

 its general portrait, as well as in the structure of its stomach, it has a near re 

 semblance to the camel ; in its voice, instead of a whistle, it has a grunt, like 

 that of the hog ; in its disposition, it is as easily tamed as the horse, and like 

 him may be employed, and often has been, as a racer, though in speed it outstrips 

 the swiftest race-horse in the world. Adanson asserts, indeed, that it will do 

 so when made to carry double ; and that, when at the factory of Podore, he had 

 two ostriches carefully broken in, the strongest of which, though young, would 

 run swifter, with two negroes on his back, than a racer of the best breed. 



Yet widely different is the mechanism of the stomach in birds of flight that 

 feed on vegetables : nor could any contrivance be better adapted to unite the 

 two characters of strength and levity. Instead of the bulky and complicated 

 compartments of the membranous stomach of ruminant animals, we here meet 

 with a thick, tough, muscular texture, small in size, but more powerful than 

 the stoutest jaw-bone, and which is usually called GIZZARD. 



It consists of four distinct muscles, a large hemispherical pair at the sides, 

 and two smaller muscles at the two ends of the cavity. These muscles are 



* Valisnieri, Anatomia, &c. p. 159, 1713. 



