GENERAL ORNITHOLOGY 



calibre of the tube, nor is the latter sacculated as in mammals. 

 The former is considered to extend from the pylorus to the ccuca 

 (structures to be presently noticed). Above the ca^ca the intestine 

 commonly receives its foldings and windings ; below them it usu- 

 ally proceeds more directly, or quite straight, to the cloaca, forming 

 literally a "rectum"; but in the ostrich this ultra-csecal tract is 

 longer than the rest, and convoluted. The cis-c£ecal portion is con- 

 ventionally divided into dnodcwun, jejunum, and ileum ; there is, 

 however, no positive anatomical distinction of these parts in any 

 animal with which I am acquainted. In birds, a " duodenum " is 

 perhaps as distinct as ever ; it forms the most constant duplication 

 of the intestine, the pancreas being lodged in this duodenal fold (Fig. 

 101, ^, I, m, n). The course of the intestine is otherwise veiy vari- 

 ous in diiferent birds. The upper end, near the pylorus, receives the 

 liepatic and pancreatic ducts ; and food is chylijied after impregna- 

 tion with the biliary and pancreatic fluids ; a process furthered by 

 the proper secretions of the intestinal follicles. The chyle is drawn 

 oft' by the hideals already described (p. 295), and the unassimilable 

 refuse of the food becomes excrementitious. 



Caeca (Lat. ccecus, blind, in the nom. pi. cceca ; sing, ccecum). — 

 The " ]>lind guts," so called because they end in culs-de-sac, are of 

 two kinds. One is the vmhllical ca'cum, or vitelline caxwn, a rudi- 

 mentary, or rather vestigial, structure, the remains of the open duct 

 by which the cavit}' of the umbilical vesicle (an embryonic organ) 

 communicated with that of the intestinal tract. It is ordinarily 

 not to be noted at all ; but it is said by Owen to have been found 

 half an inch long in the gallinule, an inch in the bay ibis, and 

 dilated into a sac an inch in diameter in the Apteryx. The 

 structures ordinarily called ca'co, or coxa coli, for they are usually 

 paired, are pouches or diverticula which set off from the intestine 

 proper at the junction of the ileum with the colon ; but there is 

 nothing in the intestine itself to mark this point, so that when 

 cseca are absent, as frequently happens, no distinction of ileum from 

 colon or rectum is appreciable. No other part of the intestinal tract 

 is so variable as the ccecal : so that j^resence or absence of these 

 appendages furnishes zoological characters nowadays taken very 

 commonly into account in framing genera and families. There are 

 no cseca, as in the turkey-buzzard and some pigeons ; there is a 

 single small caecum in herons. From a condition of extremely 

 small size, like little buds upon the intestine, cseca are found to 

 elongate to extraordinary dimensions ; and the large specimens are 

 frequently saccate or clubbed, with slender roots. In geese and 

 swans the cseca are a foot long, more or less ; in some grouse they 

 are said to be a yard long. In the ostrich the mucous membrane 

 is thrown into a spiral fold. However developed, the physiology 



