170 ANATOMY OF VERTEBRATES. 



or folded concentrically in a mass, as in the Curlew and Fla- 

 mingo. In the latter species the duodenal fold is four inches 

 in length ; then the small intestines are disposed in twenty-one 

 elliptical spiral convolutions, eleven descending towards the rectum 

 and ten returning towards the gizzard in the interspaces of the 

 former. 



Many of the Natatoi^es present a concentric disposition of the 

 folds of the small intestines similar to the Flamingo. 



The arrangement of the muscular fibres of the intestine is the 

 same as in the oesophagus, the external layer being transverse, the 

 internal lono;itudinal. 



The villi of the lining membrane manifest an analogy with the 

 covering of the outer skin, being generally much elongated, so as 

 to present a downy appearance when viewed under water. There 

 are, however, great varieties in the shape and length of the villi. 

 In the Emeu they consist of small lamellae of the lining mem- 

 brane folded like the frill of a shirt. In the Ostrich the lamella) 

 are thin, long, and numerous. In the Flamingo they are short 

 and arranged in parallel longitudinal zig-zag lines. 



In many Birds a diverticulum is observed in the small in- 

 testine, which indicates the place of attachment of the pedicle of 

 the yolk-bag in the embryo, fig. 79, m.. We have found this pro- 

 cess half an inch in length in the Gallinule, and situated seven- 

 teen inches from the pylorus : in a Bay Ibis (^Ibis falcinellci) 

 the vitelline coecum was an inch in length: in a young female 

 Apteryx it dilated into a sac, about an inch in diameter, with a 

 yellomsh stratum of the remains of the yolk.^ 



The Birds in which the cmca coli have been found vv^anting are 

 comparatively few, though such examples occur in all the orders. 

 These exceptions are most frequent among the Scansores, in 

 which the coeca are absent in the Wrynecks, the Toucans, the 

 Touracos, the Parrot- tribe, and according to Cuvier in the Wood- 

 peckers.^ In the Insessores the cocca are deficient in the Hornbill 

 and the Lark. Among the Grallatores, we have found them 

 Avanting in a Spoonbill. In the Natatores they are absent in the 

 Cormorant. The Herons, Bitterns, and, occasionally, the Grebes 

 aiford the rare examples of a single coecum, which is also remark- 

 ably short. 



In the Raptores the diurnal and nocturnal tribes differ re- 

 markably in the length of the coeca. They are less than half 



' xr. 



- In the Popinjay (Picus viridis, Linn.) wc have found two small cuica, so closely 

 adhering to the intestine as easily to be overlooked. 



