43S TEE DIGESTIVE APPARATUS IN B1BD8. 



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. This 

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

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

 two gizzard muscles are replaced by a tliin 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 UTiiforra throughoiit iis wliole 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, wliich repiesents the duodenum, 

 and whose two branches, lying side by side, are pnallel to each other lilte the colic 

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

 intestine includes the pancreas between its two brandies. 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 tlie abdominal cavity. 

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

 small iidestine 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 smdl tubercles placed on tlie track of the intestinal tube, do not measure 

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

 cuh-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 tlie anus. There are always alimentary matters in these sacs, these becoming 

 introduced, in following a. retrograde course, by the same almost unknown raechanisin 

 which presides over the accumulation of spermatic fluid in tlie vesiculaj si-minnles. Ac- 

 cording to the majority of naturalists, these two appendages, althougli described as cxca, do 

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

 nothing more than a small particular appendi.K placed on the track of the intestine, in fiont 

 of thn free extremity of the above-mentioned cuh-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 (lig 221, 12') corresponds 

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



The redum (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 reo-ion 

 this viscus is terminated by a dilatation, the cloaca (fig. 221, 10), a vestibule common 

 to the d'gestive 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 

 sucoentric ventricle. In the Pigeon, this gland is provided with a gall-blrflder 

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

 tlie excretory apparatus is not altogether identical with that observed in Maiffliials 

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

 to>vards the extremity of the second branch of the duodenal loop. One prooeeding 

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

 duct, remains independent of the Litter, 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 cystic canal is a brancli of this duct 

 (fig. 221, 22). 



Pancreas (Fig. 221, 23).— In the Gallinaae, this gland is very developed, lono-, and 

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

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

 membranes, a little in front of the hepatic canal. 



Spleen.— Th.\s is a small, red-coloured, disc-shaped body, placed to the rin-lit of the 

 stomachs, on the limit of the gizzard and succentric ventricle. ° 



