316 STRUCTURE AND CLASSIFICATION OF BIRDS 



adult there is down upon the apteria. The pterylosis,. as 

 figured by Nitzsch, is almost exactly like that of the pigeons, 

 but there are no neck spaces. The beak has no soft ' cere,' 

 such as exists among the pigeons. 



Gadow has contrasted the crop of the sand grouse with 

 that of the pigeon. In the former it is a simple dilatation of 

 the anterior and lateral walls of the oesophagus, without any 

 constriction in the middle line. In the pigeons, on the other 

 hand, the crop consists of two symmetrical swellings of the 

 oesophagus, between which is continued the oesophagus. The 

 intestinal coils have, according to Mitchell, an ' extremely 

 primitive character.' The resemblanae to the intestine of the 

 pigeons is great. The Pterocletes differ from the pigeons 

 in the large size of the ccEca. The lining of the caeca is 

 marked by about six longitudinal folds, according to G-adow, 

 but according to Paekee no less than twelve. In Pterocles 

 the right lobe of the liver is about three times the size of the 

 left. A gall bladder is always present. . Figs. 17 and 18 

 (p. 33) show some variations in the positions of the liver and 

 pancreatic ducts in the sand grouse, which are taken from 

 Gadow's paper upon the anatomy of this group. 



The syrinx (of Pterocles) is not in the least like that of 

 the ColumbaB. The extrinsic muscles are perfectly symmetri- 

 cal, and the intrinsic muscles are enormously developed. The 

 ordinary pair present in the Columbse are attached to what 1 

 regard as the first bronchial semi-ring, and are not specially 

 large ; the second pair ' are only visible on the posterior 

 aspect of the windpipe ; they are two large fusiform muscles 

 which are inserted in common into the middle line of the 

 trachea, near to its termination. 



The muscles of the hind limb have been described in some 

 detail by Gadow. 



The muscle formula is complete, being thus expressible, 

 on Gabbod's notation, by the letters ABXY-H. There is 

 only one peroneal, the longus, which has the usual attach- 

 ments to the ankle and to the flexor perforatus. 



' Pterocles arenarms ; it appears that P. alchata has not the second larger 

 pair. 



