THE DIGESTIVE AFFABATUS IN BIBBS. 437 



In GalUnacie (Fig. 221, 3. 4, 5), this dilatation does not exist; but the oesophagus 

 presents in its course, and immediately before entering tlie chest, an ovoid membranous 

 pouch named the crop (or inglumes.) In the oesophagus of these birds, then, we find 

 two distinct tections, joined end to end — one superior or cervioul, the other inferior or 

 thoracic, on the limit of which is the a-op. 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 ; iifter wliich it is passed into the succentric ventricle by the contractions of the 

 Sxternal membrane of the crop, aided by a wide subcutaneous cervical 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. "Otherwise, singular changes are observed in the apparent structure of its 

 walls in the male as well as in ihe female, during incubation, or during the first weeks 

 after hatching." (Hunter was the first to observe this : — ' Observations on Certain Parts 

 of the Animal Economy,' London, 1792). "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 interuiil surface is divided by folds or ridges, which cross 

 each other, and form triangular meshes ; while an apparently milky fluid is poured- out 

 from the secretory pores into the cavity of the crop. Pigeons txelusively nourish their 

 young with this fluid during the first three days of their existence." ' 



Stomach — The stomach presents numerous variations in birds. Its simplest form is 

 seen in the heron, pelican, petrels, etc., where it is a single sac provided with a thick 

 zone of glands around the enti-ance of the oesophagus, which secrete the gastric juice. 

 But in the majority of the other sj)ecies, and particularly in our domesticated birds, the 

 disposition of the stomach is modified and complicated ; the glandular zone destined for 

 the gastric secretion forms a special compartment — the succentric ventricle, and this is 

 followed by a second reservoir^the gizzard, which is remarliable for the strong muscular 

 constitution of its walls. The first is also named the glandular stomach, and the second 

 the muscular stomach. 



Glandular stomach, or succentric vevfricle (^proventriculus) (Pig. 221, 6). — This is an 

 ovoid sac placed in the median plane of the body, between the two lobes of the liver, and 

 beneath the aorta. Its anterior extremity receives the insertion of the oesopliagus; the 

 posterior is continued by the gizzard. Tiie volume of this stomach is inconsiderable, and 

 its cavity is very narrow ; the aliment does not accumulate in it, but merely passes 

 tlirough, carrying with it the acid juice which afterwards dissolves its protein elements. Its 

 walls have three tunics : an external or peritoneal ; a middle, formed of white muscular 

 fibres, continuous with those of the oesophagus ; and an internal, of a mucous nature, per- 

 forated by orifices for the passage of the gastric juice. These are small cylinders placed 

 perpendicularly to the surface of the stomach, closely laid against one- another, like the 

 microscopic glands of Lieberkiihn, and contained iif the cellular layer uniting the inner 

 to the middle tunic. Tlie glandular structure of this receptacle sufficiently demonstrates 

 that it should be assimilated to the right sac of the stomach in Solipeds, and thtiefore 

 must be regarded as the true stomach. 



Gizzard, or muscular stomach (ventriculus hulbosus} (Fig. 221, 7). — Much more volu- 

 minous than the preceding, this stomach is oval in form, depressed oh each siile. and 

 situated behind the liver, being partly covered by the lateral lobes of that gland. Above, 

 and to the right, and at a short distance from each other, are seen the insertion of the 

 succentric ventricle and the origin of the duodenum. The cavity of the gizzard always 

 contains food mixed with a large quantity of silicious pebbles, whose use will be indicated 

 hereafter. 



This viscera is composed of the three tunics -which form the walls of all the 

 abdominal reservoirs. The internal, or mucous, is distinguished by the thickness and 

 extraordinary induration of its epidermic layer, which presents nearly all the characters 

 of horny tissue, and is so easily detached from the mucous ehorium that it is often 

 regarded as a special membrane. On the adherent face of this corium are applied two 

 powerful red muscles — a superior and inferior, occupying the borders of the organ, and 

 whose fibres, dispo.sed in flexures, pass from side to side, and are inserted into a strong, 

 nacrous aponeurosis on Ihe lateral surfaces of the organ. Outside this contractile 

 apparatus is a thin peritoneal envelope. 



The gizzard is the triturating apparatus of birds. When the aliment reaches its cavity 

 it has not yet submitted to any disaggregation, but here it meets witli all the conditions 



• Duvernoy. ' Legons d'Anatomie Compare'e de G. Ouvier.' 2nd Edition. 

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