STRUCTURE OF BIRDS. 55 



cesophagus contracts to about three-fourths of an inch in diame- 

 ter, and at its termination, ??^, enlarges to ten-twelfths, forming 

 the proventriculus, m^ which is about an inch long. 



At its upper part, the oesophagus has a slight outer layer of 

 inconspicuous longitudinal muscular fibres. In its whole length, 

 it is encircled by transverse fibres, forming a distinct muscular 

 coat. The inner or mucous coat is thrown into longitudinal 

 rugoe, when the organ is contracted ; otherwise it is smooth 

 and even. 



At this stage of the description, it must be mentioned that 

 the tube extending from the mouth, a, 5, to the stomach, w, o, 

 is by some considered as properly speaking the oesophagus, of 

 which the dilatation, or crop, k^ and the thickened part or pro- 

 ventriculus, ?», are only parts ; while others maintain that the 

 crop, ^, is in reality the first stomach, and the proventriculus, 

 w, the second ; n^ o, being the third. The oesophagus, then, 

 according to these observers, is that part which extends from 

 the mouth to the commencement of the crop ; and the tubular 

 pai-t between the crop and the proventriculus John Hunter 

 named the second or low^er oesophagus. Were these views cor- 

 rect, the Peregrine Falcon has no proper cesophagus, for its 

 dilatation begins at the mouth. As in many other questions 

 of this nature, " much may be said on both sides f' for which 

 reason it may be judiciously referred to the debating societies. 

 In the meantime, the entire tube, wdiether dilated or not, from 

 the mouth, a, to the stomach, w, I shall consider as the oeso- 

 phagus. 



At the lower part of the oesophagus, just before it joins the 

 stomach, it presents a second enlargement, m, named the pro- 

 ventriculus. The calibre of this portion, or organ, is generally 

 less than that of the adjoining portion of the oesophagus, so that 

 the greater diameter of the proventriculus is made up by a 

 thickening of its walls, there being interposed between its mus- 

 cular and mucous coats numerous glandules or sacs, placed la- 

 terally in apposition, nearly at right angles to the surfaces of these 

 coats. Fig. 8. represents a longitudinal section of the thickest 

 part of the walls of the proventriculus, of the natural size : a, the 

 outer or muscular coat ; 6, the inner or mucous coat ; the glau- 



