438 THE DIGESTIVE APPARATUS l\ /;////. 



indispensable to the accomplishment of thU act: two > ti -!;(. 



corneous layer spread over the internal surface of the visccm. -ivinir i-> it tin- rigidity 

 necessary to resist the enonnu.s pressure exercised un it- c..nt' -nt-i : ,-irnl .-i 

 pebbles -\vrit.ihlc artilicial teeth which an admirable instinct C.UIM -s birds to swallow, 

 uini between which, l>y the cffits of the tiiturating muscles, th" food js l>ruis.-d. This 

 triturating action of the gizzard is only effected in birds fed on him I eoriact on> aliim-nt, 

 such as tin- various kind of grain. It wnnld l>c n>. lc .-.- in birds of prey, in which the 

 two gizzird muscles are replaced by a thin fleshy membrane of uniform thu-K 

 showing that the presence of these nm-drs is subordinate, to the kind of alimentation. 



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

 nnture of the food : very short in birds of prey, it is notably elongated in omniv 

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

 and it is difficult to establish in birds the VHrions distinctions recognised in tin- iii' 

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

 and whose two branches, lying side by side, are pmdlel to each other like th. 

 flexure of Solipeds. Fixed by a short mesenteric frtenum 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 pariet. s by a 

 long mesentery, ami 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 /i<>rti<ni nf the 

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



Tin- terminal part of this floating intestine lies beside the duodenal loop, an 1 is 

 flanked by the two appendages disposed like cxca. These, scaict-ly 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; th'-y arc two narrow 

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

 inwards the origin of the intestine, while the other extremity opens into tin- intestinal 

 canal near the anus. There are always alimentary matters in these .aes. I!,.-M- U'c.iming 

 introduced, in following a retrograde course, by the same almo.-t unknown nn-clianisiu 

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

 I'tirdisi^ to the majority of naturalists, these two appendages, although describt-d ascreo, do 

 not represent the reservoir bearing that designation in Mammals. This reservoir i.-, 

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

 of the free extremity of the above-mentioned cuh-de-eac, and which is only to be found 

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

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

 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 caeca. Placed in the sublumbar region, 

 this viscus is terminated by a dilatation, the cloaca (fig. 221, If.), 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 

 Fftbricius, and the deferent canals. 



ABDOMINAL APPENDAGES OF THE DIGESTIVE CANAL. Liver (Fig. 221, lit, 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 gi/znrd 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. 13ut the amngement flf 

 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 choledi<- dn<-t ; the other, th. 

 duct, remains independent of the Litter, and opens behind it. It curries into the dr. 

 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 branch of this duct 

 (fig. 221, '22). 



Panrreas (Fig. 221, 23). In the GalUwii-n , thi- uland is very developed, long, and 

 narrow, and is c .mpri-ed in the duodenal loop or flexure; at the extremity m xt the 

 gizzard it has two principal excretory ducts, which sepaiately pierce the int. 

 membranes, a little in front of the hepatic c.itwl. 



Spleen. This is a mnall, red-coloured, di.M--..ha] d \\\. placed to the right of th. 

 f-tomachs. on the limit of the gizzaid and bucccntric ventricle. 





