512 THE DIGESTIVE APPARATUS OF BIRDS. 



as representing the parotids, any more than the glands of the cheeks and lips. 

 Duvernoy ^ categorically assimilates it with the latter. 



The sublingual glands lie in the median line throughout nearly their whole 

 extent, and form an apparently single and conical mass, whose apex occupies the 

 re-entering angle formed by the union of the two branches of the lower maxilla. 



According to Duvernoy, the submaxillary glands are represented by two very 

 small organs situated behind the preceding. Their existence, however, is far 

 from being general ; for among common poultry, the Turkey was the only bird 

 in which Duvernoy observed these submaxillary glands. 



Pharynx (Fig. 305, 2). — This cavity is not distinct from the mouth, the 

 soft palate being entirely absent in Birds. On its superior wall may be remarked 

 the guttural orifice of the nasal cavities : a longitudinal slit divided into two 

 by the inferior border of the vomer. Below is another less extensive slit, the 

 entrance to the larynx, and which is remarkable for the complete absence of the 

 epiglottidean operculum. 



(Esophagus. — This canal is distinguished by its enormous calibre and great 

 expansibility. Its walls are very thin, and contain in their substance lenticular 

 glands, easily seen in an inflated oesophagus, in consequence of the tenuity and 

 transparency of its textures. 



At its origin, the oesophageal canal is not separated from the pharynx by any 

 constriction ; in its course it lies alongside the long muscle of the neck, and the 

 trachea ; its terminal extremity is inserted into the first compartment of the 

 stomach, or succentric ventricle, after entering the thorax and passing above 

 the origin of the bronchi, between their two branches. 



In Palmipeds, the oesophagus is dilated in its cervical portion in such a 

 manner as to form, when its walls are distended, a long fusiform cavity. 



In Gallinacce (Fig. 305, 3, 4, 5), this dilatation does not exist ; but the 

 oesophagus presents in its course, and immediately before entering the chest, an 

 ovoid membranous pouch named the crop (or iiigluvies). In the oesophagus of 

 these Birds, then, we find two distinct sections, joined end to end — one superior 

 or cervical, the other inferior or thoracic on the limit of which is the crop. The 

 latter does not differ in its structure from the oesophagus, and is a temporary 

 reservoir for the food swallowed by the animal during its meal, and where it is 

 softened by being impregnated with a certain quantity of fluid ; after which it is 

 passed into the succentric ventricle by the contractions of the external membrane 

 of the crop, aided by a wide subcutaneous cervicle muscle which covers that 

 reservoir. 



In Pigeons, the crop is also present ; but it is divided into two lateral 

 pouches, and exhibits glandular eminences towards the common inferior opening 

 of these sacs into the oesophagus {aquiparous glands). Singular changes are 

 observed in the apparent structure of its walls in the male as well as lq the 

 female, from the eighth to the twentieth day of incubation, or during the first 

 weeks after hatching, which coincide with the appearance of a kind of secretion 

 which, when regurgitated, serves to nourish the young birds. At this period, 

 the membranes of the crop become thickened ; the vessels, more numerous and 

 more apparent, are redder, and the glands more developed ; the folds or ridges 

 of the mucous membrane become more marked, and in their interspaces are deep 

 depressions where an apparently milky fluid accumulates, and which is derived 

 from the active proliferation of the epithelium and its concomitant fatty 

 ' Cuvier, Anatomie Cum,par€e. 2nd Edition. Paris : 1836. 



