58 INTRODUCTION. 



tached to tlic mesentery, turns back, and forms a small fold ; 

 then forms a number of convolutions, ?/, r% occupying the space 

 behind or above the stomach ; runs up behind that organ, then 

 forms a small fold, and passing backwards along the sacrum, 

 forms the rectum, zc, Avhich terminates at the anus, a\ 



The duodenal portion of the intestine has a diameter of about 

 five-twelfths of an inch ; the remaining part gradually dimin- 

 ishes to three-twelfths, until about nine inches from the extre- 

 mity, when it slightly enlarges. The terminal part is named 

 the rectum or large intestine ; and being only partially seen in 

 Fig. 5, at ii\ ^, is figured apart. 



The rectum, Fig. 6, a, b, is that part of the intestine com- 

 mencinof fit the coeca, a, and terminatinsj at the anus, b. It 

 generally enlarges at once in the rapacious birds, and continues 

 to widen, but in the Peregrine Falcon is not much wider than 

 the duodenum. It is seen to dilate at the end, so as to form 

 an elli^^tical cavity, ^, b. This part, which has a rim or valve 

 internally at <?, is an imperfect kind of bladder, into which 

 open the two ureters, ^, d^ upon a prominent fiap or rim at e. 

 Immediately below them is seen the larger a2:>erture of the 

 Bursa Fabricii, an oblong sac lying behind the extremity of 

 the rectum, and secreting a mucous fluid. The space between 

 the edge on which the ureters enter and the extremity of the 

 gut at ^, is usually called the cloaca ; and into it also the ovi- 

 duct enters. 



Besides the peritoneal covering, the intestine has a muscu- 

 lar and an inner or mucous coat. The former is thickest in 

 the duodenal portion, the inner surface of which is delicately 

 villous. On the rest of the small intestine internally are long, 

 extremely slender villi, which, towards its lower part, become 

 more sparse. The inner surface of the coeca has a cellular 

 appearance ; that of the rectum is furnished at its anterior 

 part with numerous mucous crypts. The cloaca is smooth 

 within. 



This description and the figures are taken from a male bird 

 shot in December 1836, on the Pentland Hills, near Edin- 

 burgh. Some persons being fond of knowing the numerical 

 proportions of the organs of birds, I subjoin the measurements. 



