290 NATURAL THEOLOGY. 



ment of the nerves supplying these parts disorders 

 the whole train of actions. We have to show, 

 then, how this function, deficient in the bird, is 

 compensated by internal structure. 



The gizzard is a fleshy stomach, the exact sub- 

 stitute for the muscles of the jaws, and teeth. Its 

 substance consists cf a strong muscle ; the dark 

 part of the gizzard being the muscle, and the shi- 

 ning part of it the tendon to which the muscular 

 fibres are attached. There are^ in fact, two mus- 

 cles with a central tendon ; it is what anatomists 

 call a digastric or double-bellied muscle. The 

 cavity within this muscle is lined with a dense, 

 rough, insensible coat, and there are always to be 

 found contained in it small stones, generally of 

 quartz, if it be within the reach of the creature's 

 instinct to obtain them. The grains are mixed 

 with these portions of stone ; and if we put our 

 ear close to a bird, we shall hear the grinding mo- 

 tions going on as distinctly as the noise of the 

 horse's jaws in the manger. In fact, this digastric 

 muscle or gizzard is equivalent to the muscles of 

 the jaws, and the pebbles are a fair equivalent to 

 the teeth, with this advantage, that when they are 

 ground down, the instinct of the bird supplies it 

 with more. It picks up some small portions of 

 gravel with as much alacrity as it will the grain 

 itself. Some have supposed that this was sheer 

 stupidity in the fowl ; but here surely instinct is 

 better than reason. 



When we recollect the provisions against attri- 



