724 AVES. 



Its cavity is very small, and lined with a dense, coriaceous cuticular 

 stratum ; and its substance is almost entirely made up of two dense and 

 enormously powerful masses of muscle, the fibres of which radiate from 

 two central tendons (fig. 358, c), situated upon the opposite sides of the 

 viscus. The action of these lateral muscles will obviously grind and 

 crush with great force whatever is placed in the central cavity, a pro- 

 cess that is materially expedited by the presence of hard and angular 

 pebbles, swallowed for the purpose, by the assistance of which the con- 

 tained food is speedily comminuted. 



(2050.) Another and much feebler set of muscles (d) bounds the 

 cavity of the gizzard in the intervals between the great lateral masses 

 which, receiving the food from the proventriculus, perpetually feed this 

 living mill, and retain the material to be ground within the influence of 

 the crushers until it is properly prepared, when other fibres, acting the 

 part of a pylorus, allow it to pass on into the duodenum (e). 



(2051.) The intestinal canal of Birds is, as in other classes, very 

 variable in its relative length as compared with that of the body ; its 

 calibre is pretty equal throughout, and the division into large and small 

 intestines can scarcely be said to exist. Commencing from the pylorus, 

 the duodenum (fig. 359, d h) is always found to make a long and very 

 characteristic loop, embracing the lobes of the pancreas (e e) ; and then, 

 after sundry convolutions, the intestine is continued to its termination 

 in the cloaca. The division between the large and small intestines is 

 indicated by the presence of one, or more generally two, ca3cal append- 

 ages, which communicate with the cavity of the gut at no great distance 

 from its cloacal extremity. 



(2052.) In Birds, the auxiliary secretions subservient to the digestive 

 process are the salivary, the gastric, the hepatic, and the pancreatic. 



(2053.) The salivary apparatus varies much in structure and dispo- 

 sition in different tribes. In its simplest form it consists of distinct 

 secerning follicles, placed immediately beneath the mucous membrane 

 of the mouth, into which the secretion is poured by numerous orifices. 

 In the Gallinaceous birds the glands assume a conglomerate character. 

 In the Turkey there are two pairs * : the first pair forms a cone, having 

 its apex directed towards the extremity of the beak ; and the two glands 

 of the opposite sides touch each other along the mesial line through 

 almost their entire length, filling up anteriorly the angle of the lower 

 jaw. These glands are situated immediately beneath the skin, but in 

 front they touch the mucous membrane of the mouth ; and their secre- 

 tion is poured into the buccal cavity by several orifices. The second 

 pair of glands is smaller, of an elongated form, and is placed above the 

 posterior third of the former ; this is immediately in contact with the 

 mucous lining of the mouth. 



(2054.) In the Woodpeckers the glands that secrete the fluid whereby 

 * Cuvier, 1*90118 d'Anat. Comp. torn. iii. p. 221. 



