LESSON 49.] 



NUTRITION IN BIEDS. 



175 



another but slight enlargement (c) before it enters the stomach ; this 

 second sac is called the " proventriculus " (pro, before ; ventricubts, 

 the stomach). This latter organ secretes a gastric fluid proper, which 

 additionally prepares the food for the stomach's action. The giz- 

 zard, or true stomach of these birds (d) next succeeds, and if its 

 structure be found on investigation to be peculiar, so at least is its 

 function. Examined carefully, it will be found to possess two pairs 

 of muscles ; of these, one pair is moderately, while the other is most 

 immoderately, developed ; the interior, too, is lined with a hard, cal- 

 lous, non-vascular, perfectly insensible, membrane. 



763. The action of these muscles is to press the sides of the 

 stomach (gizzard) firmly together, and produce and sustain a lateral, 

 grinding motion, by which means the hard food may become thorough- 

 ly triturated (reduced to a very fine pulp). To assist this most 

 remarkable process, these birds always swallow small particles of 

 flint, for without its agency the probability is that the perfect reduc- 

 tion of the food could not be accomplished. These flinty particles, 

 combined with the constant, firm, lateral motion of the muscles, and 

 aided by the insensible lining membrane of the gizzard, form an ex- 

 cellent apparatus for the purpose required. 



764. Those persons who keep Canaries, and other singing birds, 

 instead of sprinkling fine gravel on the bottom of the cage, that the 

 poor birds might help themselves to flint, to assist their digestion, 

 usually give them a piece of Cuttlefish-bone (Carbonate of lime !), 

 which is useless. 



765. The consequence is, .the poor creatures sicken (of dyspepsia) 

 and die ; if any one will make the experiment, and try the effect of 

 some minute particles of .silica on their favorite song birds, the ex- 

 treme greediness with which it will be consumed will speedily assure 

 them of the necessity for its continuance. 



766. The liver, of fair dimensions (e), discharges its secretion, 

 by its proper duct, into the duodenum ; the 



well-formed gall bladder (jf ), and a pan- 

 creas, or sweetbread (g)- are also met 

 with. The duodenum (h) succeeds the 

 stomach, or gizzard ; if the latter be found 

 devoid of blood-vessels, the like cannot be 

 said of this commencement of the small 

 intestines, for, on the contrary, its inner 

 surface is densely covered with villi (like 

 the pile of velvet, and giving a velvety 



FIG. 280. 



VilU of the duodenum of a Fowl. 



