336 CLASS XVI. 



the right and one on the left side of the lowest portion of the 

 oesophagus. Behind the crop the oesophagus is generally nar- 

 rower than in its anterior part, and afterwards passes into the 

 stomach. 



The stomach of birds consists of two divisions. The first di- 

 vision, the glandular stomach [proventriculus, hulhus glandidosus) , 

 has usually the form of an oval expansion of the lowest part of the 

 oesophagus. Under the external membrane, which, as a duplica- 

 ture of the peritoneum, covers both stomachs, there lies in the glan- 

 dular stomach a thin muscular coat, and to this succeeds on the 

 inside a layer of numerous glandules, whose apertures are visible to 

 the naked eye on the inner surface of the stomach. These glands 

 are small elongated blind sacs, which stand as eversions of the 

 raucous membrane with their long axis perpendicular to the long 

 axis of the stomach, and thus are nearly horizontal ; sometimes 

 their blind extremity is branched. 



In the glandular stomach the gastric juice is secreted ; at the 

 inferior extremity the little glands diminish in number, or even dis- 

 appear entirely before the commencement of the second division. 

 This second division is named the muscular stomach. The muscu- 

 lar tunic is here developed in a much greater degree ; its fibres 

 radiate from two tendinous plates, of which the one is situated on 

 the anterior, the other on the posterior surface of the stomach. 

 Internally, this stomach is covered with a horny epitJieUum, which, 

 particularly in the gallinaceous birds, where the muscular tunic is 

 also very thick, possesses much rigidity ^ The muscular stomach 

 is round and flat; in birds of prey it has a thinner muscular tunic. 

 By the action of the muscular fibres the food is pressed and bruised 

 between the horny covering of the inner surface, which in other 

 animals, especially in mammals, is efi'ected previously by masti- 

 cation. According to A. Retzius, this muscular stomach or giz- 

 zard is to be considered as a development of that part of the 

 stomach of man and mammals, which is called by Willis the 

 antru7n jyylori. 



1 Sometimes on this horny covering spines are placed in longitudinal rows, as in 

 the muscular stomach of the Condor (Harlan American Philos. Transact, iii. 2, 

 p. 466), or tooth-shaped tubercles, as in Procellana glacialis, Carus Tai. Anatomiam 

 camp, illustrantes, iv. Tab. vi. figs. 15, 16. 



