514 THE DIGESTIVE APPARATUS OF BIRDS. 



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 entrance of the oesophagus, which secrete 

 the gastric juice. But in the majority of the other species, and particularly in 

 our domesticated Birds, the disposition of the stomach is modified and comphcated ; 

 the glandular zone destined for the gastric secretion forms a special compartment 

 — the surcentric ventricle, and this is followed by a second reservoir — the gizzard, 

 which is remarkable 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 ventricle {proventriculus) (Fig. 305, 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 oesophagus ; the posterior is continued by the gizzard. The volume of 

 this stomach is inconsiderable, and its cavity is very narrow ; the aliment does 

 not accumulate in it, but merely passes through, 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, perforated 

 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 in the connective tissue 

 layer uniting the inner to the middle tunic. The glandular structure of this 

 receptacle caused it to be regarded as the true stomach in Birds ; but Jobert has 

 shown that the real gastric juice is secreted in the gizzard. 



Gizzard or muscular stomach {ventricidus bulbosus) (Fig. 305, 7). — Much 

 more voluminous than the preceding, this stomach is oval in form, depressed on 

 each side, 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, the use of which will be indicated hereafter. 



This viscus is composed of the three timics 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 which results from the accumulation of the 

 products secreted by the epithelium. The latter is spheroidal, and is so easily 

 detached from the mucous chorium 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, disposed in flexures, pass from side to side, and are inserted into a strong, 

 nacrous aponeurosis on the 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 with 

 all the conditions indispensable for the accomplishment of this act : two energetic 

 compressor muscles, a corneous layer spread over the internal surface of the 

 viscera, giving to it the rigidity necessary to resist the enormous pressure exercised 

 on its contents ; and silicious pebbles — veritable artificial teeth — which an 

 admirable instinct causes Birds to swallow, and between which, by the effort 

 of the triturating muscles, the food is bruised. This triturating action of the 



