474 MANUAL OF ZOOLOGY sect, xii 



{hu, hu'), which it depresses. The elevation of the wing is 

 performed, not, as might be expected, by a dorsally placed 

 muscle, but by the sub-davius {sb. dv), arising from the 

 anterior part of the body of the sternum, dorsal to the 

 pectoralis, and sending its tendon {sb. dv') through the 

 foramen triosseum to be inserted into the dorsal aspect of 

 the humerus. In virtue of this arrangement, the end of the 

 foramen acting like a pulley, the direction of action of the 

 muscle is changed, the backward pull of the tendon raising 

 the humerus. 



Digestive Organs. — The mouth (Fig. 287) is bounded 

 above and below by the horny beaks, and there is no trace 

 of teeth. The tongue {tug) is large and pointed at the tip. 

 The pharynx leads into a wide and distensible gullet {gul), 

 which soon dilates into an immense reservoir or crop {crp) 

 situated at the base of the neck, between the skin and the 

 muscles and immediately in front of the sternum. In this 

 cavity the food, consisting of grain, undergoes a process of 

 maceration before being passed into the stomach. From 

 the crop the gullet is continued backwards into the stomach, 

 which consists of two parts, the proven triculus {ptvn) and 

 the gizzard {giz)- The proventriculus appears externally 

 like a slight dilatation of the gullet, but its mucous mem- 

 brane is very thick and contains numerous gastric glands 

 so large as to be visible to the naked eye. The gizzard has 

 the shape of a biconvex lens ; its walls are very thick and 

 its lumen small. The thickening is due mainly to the im- 

 mense development of the muscles which radiate from two 

 tendons, one on each of the convex surfaces. The epi- 

 thelial lining of the gizzard is very thick and horny, and 

 of a yellow or green colour : its cavity always contains small 

 stones, which are swallowed by the bird to aid the gizzard 

 in grinding up the food. 



