STRUCTURE OF BIRDS. 57 



by the proventricular fluid ; and sometimes the whole is re- 

 duced to a pulpy substance ; so that for a long time I con- 

 sidered the internal surface of the stomach of rapacious birds 

 to be entirely destitute of epithelium or cuticle ; but have lived 

 long enough to see my error. In the Peregrine Falcon, this 

 epithelium varies in thickness from half a twelfth to a twelfth 

 and a half of an inch, and is of a reddish- white colour. 



At its commencement the oesophagus is placed directly in 

 front when not distended, but wdien filled inclines immediately 

 to the right side, on which the crop lies. At the lower part of 

 the neck it inclines to the left side, passes into the thorax in the 

 centre, when the trachea or windpipe, ^, c?, which passes along 

 the left side, comes in front of the oesophagus, and bifurcates 

 immediately behind the base of the heart. The oesophagus con- 

 tinues inclining to the left side behind the left lobe of the liver, 

 and joins the stomach opposite the last ribs. The stomach 

 occupies the middle and left side of the abdomen, and when 

 distended fills a very large proportion of its cavity. Between 

 it and the sacrum are interposed a portion of the intestines and 

 the kidneys ; the duodenal part of the intestine lies between it 

 and the walls of the abdomen on the right side ; a portion of the 

 liver lies over it in front ; the greater part of its anterior sur- 

 face is in contact with the abdominal parietes, as is also its left 

 edge. 



The intestine comes oft' from the stomach at p^ close to its 

 upper or cardiac orifice. The entrance to it is named the py- 

 lorus, and frequently has a valvular structure, which in the 

 Peregrine Falcon presents the appearance of a rim with three 

 knobs. Fig. 11. The leng-th of the intestine is four feet three 

 inches. It first inclines to the left, />, q, along or anterior to 

 the edge of the stomach, until it nearly reaches the back, 

 and is then bent back in a parallel direction, q, r, and curves 

 forwards to pass under the right lobe of the liver at r. 

 This fold, which is named the duodenum, or duodenal curve, 

 is connected by a reflection of the peritoneum, on which lies 

 the pancreas, 5, which is a long narrow gland similarly folded 

 upon itself, and of which the ducts enter the intestine near r. 

 After receiA^ng them and the biliary ducts, ^, r, it becomes at- 



