438 THE DIGESTIVE APPARATUS IN BIRDS. 



indispensable to the accomplishment of this act: two energetic compressor muscles, a 

 corneous layer spread over the internal surface of the viscera, giving to it the rigidity 

 necessary to resist the enormous pressure exercised on its contents; and silicious 

 pebbles veritable artificial teeth which an admirable instinct causes birds to swallow, 

 and between which, by the efforts of the tiiturating muscles, the food is bruised. Thi3 

 triturating action of the gizzard is only effected in birds fed on hard coriaceous aliment, 

 such as the various kind of grain. It would be useless in birds of prey, in which the 

 two gizzard muscles are replaced by a thin fleshy membrane of uniform thickness; 

 showing that the presence of these muscles is subordinate to the kind of alimentation. 



INTESTINE. The length of the intestine varies, as in Mammals, according to the 

 nature of the food : very short in birds of prey, it is notably elongated in omnivorous 

 and granivorous birds. Its diameter is nearly uniform throughout its whole extent, 

 and it is difficult to establish in birds the various distinctions recognised in the intestine 

 of Mammalia. It begins by a portion curved in a loop, which represents the duodenum, 

 and whose two branches, lying side by side, are p irallel to each other like the colic 

 flexure of Solipeds. Fixed by a short mesenteric menum to the colon, this part of the 

 intestine includes the pancreas between its two branches. Its curvature floats freely in 

 the pelvic portion of the abdominal cavity (fig. 221, 8, 9, 10). 



To the duodenal loop succeed convolutions suspended to the sublumbar parietes by a 

 long mesentery, and which are rolled up into a single mass, elongated from before to 

 behind, occupying a middle position between the air sacs of the abdominal cavity. 

 The analogy existing between this mass of convolutions, and the floating portion of the 

 small intestine of Mammals, does not require demonstration (fig. 221, 11, 12), 



The terminal part of this floating intestine lies beside the duodenal loop, and is 

 flanked by the two appendages disposed like cxca. These, scarcely marked in the 

 Pigeon by two small tubercles placed on the track of the intestinal tube, do not measure 

 less than from six to ten inches in the other domesticated birds ; they are two narrow 

 culs-de-sac, slightly club-shaped at their closed extremities, which are free and directed 

 towards the origin of the intestine, while the other extremity opens into the intestinal 

 canal near the anus. There are always alimentary matters in these sacs, these becoming 

 introduce;!, in following a retrograde course, by the same almost unknown mechanism 

 which presides over the accumulation of spermatic fluid in the vesiculaj seminales. Ac- 

 cording to the majority of naturalists, these two appendages, although described as ceeca, do 

 not represent the reservoir bearing that designation in Mammals. This reservoir is 

 nothing more than a small particular appendix placed on the track of the intestine, in front 

 of tho free extremity of the above-mentioned culs-de-sac, and which is only to be found 

 in a small number of birds, and among these sometimes, as Guilt affirms, is the Goose. 

 According to this view, which appears to be a very rational one, the portion of intestine 

 comprised between the two blind tubes annexed to the viscera (fig 221, 12') corresponds 

 to the colon, and these tubes themselves are only dependencies of this intestine. 



The rectum (fig. 221, 15) terminates the digestive canal; it is the brief portion of 

 intestine which follows the opening of the cseca. Placed in the sublumbar region, 

 this viscus is terminated by a dilatation, the cloaca (fig. 221, 16), a vestibule common 

 to the digestive and genito-urinary passages, which opens externally at the anus, lodges 

 the penis when it exists, and serves as a confluent for the ureters, oviduct, bursa of 

 Fabricius, and the deferent canals. 



ABDOMINAL APPENDAGES OF THE DIGESTIVE CANAL. Liver (Fig. 221, 19, 20). This 

 is a voluminous gland, divided into two principal lobes a right and left, the former 

 always larger than the latter; these incompletely include, on each side, the gizzard and 

 succentric ventricle. In the Pigeon, this gland is provided with a gall-bladder 

 (fig. 221, 21) attached to the internal face of the right lobe. But the arrangement of 

 the excretory apparatus is not altogether identical with that observed in Mammals 

 which possess this receptacle ; as two biliary ducts open separately into the intestine 

 towards the extremity of the second branch of the duodenal loop. One proceeding 

 directly from the two lobes of the liver, is the hepatic or choledic duct ; the other, the cystic 

 duct, remains independent of the latter, and opens behind it. It carries into the digestive 

 canal the bile accumulated in the gall-bladder, and which arrives there by a particular 

 duct belonging exclusively to the right lobe ; the cy&tic canal is a branch of this duct 

 (fig. 221, 22). 



Pancreas (Fig. 221, 23). In the Gattinacse,, this gland is very developed, long, and 

 narrow, and is comprised in the duodenal loop or flexure; at the extremity next the 

 gizzard it has two principal excretory ducts, which separately pierce the intestinal 

 membranes, a little in front of the hepatic canal. 



Spleen. This is a small, red-coloured, disc-shaped body, placed to the right of tho 

 stomachs, ou the limit of the gizzard and fcuccentric ventricle. 



