408 THE PIGEON. PHYLUM CHORDATA 



near the same spot is the opening of the duodenum. This is a V- 

 shaped loop, between whose hmbs Hes the pancreas. The ducts 

 of this gland are three, and all open into the distal limb of the 

 duodenum, two about the middle of its length, and one, which is 

 longer than the others, near the end. There are two bile ducts, 

 which run from the large, bilobed liver and join the duodenum, 

 the wide left duct opening into the proximal limb and the narrower 

 right duct into the distal limb near the first two pancreatic ducts. 

 There is no gall bladder in the common pigeon. The ileum is a 

 much-coiled tube about two and a half feet in length. The rectum 



is about an inch and a half long. Its beginning 

 is marked by a pair of small rectal caeca ; 

 behind it opens by an anus into the cloaca 

 (Fig. 322). This has three regions separated by 

 shelves of the wall. The first and largest is the 

 /O P^ "^)j^ coprodaeum into which the rectum opens, the 



^^^-\ j^^^" small middle division is the urodaeum into 



which the urinary and generative ducts open, 

 grammatic section the third, larger, is the proctodseum ; upon 

 of the cloaca of a jts dorsal surfacc there opens in the young a 



male bird. — After , . . ^, , -A . .. r ^ 



Gadow. glandular sac, the bursa rabricn, 01 unknown 



cd., Upper region of cloaca lUnCLlOn. 



op?ns ; ^^uf, meS The digcstivc processes show some peculiar- 

 \lfiT^'"de"reZ itics. Thcrc is some digestion in the crop, 

 side ; ° M, ^'posterio? mainly by autolysis and bacterial attack, and 

 pliiMfilfopenr^ it has been shown that in the fowl the grinding 



in the gizzard is necessary for the digestion of 

 coarse corn ; finely ground corn could be dealt with by birds from 

 whom the gizzard had been removed. The gizzard contents in 

 the pigeon are highly acid (pH 2.0) but in the proventriculus the 

 acidity is less (pH 4.8), and there seems to be a poor supply of 

 pepsin. The intestinal contents at pH 5.3-5.5 are more acid than 

 in mammals. Most species of bird do not have a crop, and many 

 are without a gizzard. 



The spleen is a small red body, attached to the right side of 

 the proventriculus. 



RESPIRATORY ORGANS 



The glottis, behind the root of the tongue, opens into the 

 voiceless larynx, from which the long trachea (Fig. 321), 



