AVES. 



319 



Fig. 159. 



the macerating grains. This phenomenon is 

 the nearest approach in the class of Birds to 

 the great characteristic function, the presence of 

 whose special apparatus, the mammae, has af- 

 forded the universally recognized title of the 

 higher division of warm-blooded Vertebrata ; 

 and the analogy of the ' Pigeon's milk' to the lac- 

 teal secretion of the mammalia has not escaped 

 popular notice. In the subjoined figure one side 

 of the crop (/>), shows the ordinary structure of the 

 parts, the other (e), the state of the cavity during 

 the period of rearing the young (fig. 158). 



The canal which is continued from the in- 

 gluvies to the stomach was called by Hunter 

 the second or lower oesophagus ; at its com- 

 mencement it is narrower and more vascular 

 than that part of the gullet which precedes 

 the crop, but gradually dilates into the first 

 or glandular division of the stomach, which 

 is termed the ' proventriculus ' (ventriculns 

 succenturiatus, bulb us glandulosus, echinus, 

 infundibulum, the ' cardiac cavity' of Home), 

 (c, Jig. 156, 157, 166). 



In birds with a wide oesophagus (a, /?g.!65), 

 as the omnivorous and piscivorous tribes, the 

 commencement of the proventriculus (e, fig. 

 165), is not indicated by any change in the di- 

 rection or diameter of the tube, but only by 

 its greater vascularity, by the difference in the 

 structure of the lining membrane, and by 

 the stratum of glands which open upon its 

 inner surface, and which are its essential cha- 

 racteristic (c. fig. 

 159). Hence it is 

 by some compara- 

 tive anatomists re- 

 garded as a part of 

 the oesophagus. 



The proventri- 

 culus varies, how- 

 ever, in form and 

 magnitude in dif- 

 ferent birds. In 

 the Rasores it is 

 larger than the oeso- 

 phagus, but much 

 smaller than the 

 gizzard. In the 

 Psittacida and Ardeida (Parrot and Stork 

 tribe) it is larger than the gizzard and of a 

 different form. In the Ostrich the proventri- 

 culus is four or five times larger than the 

 triturating division of the stomach, being con- 

 tinued down below the liver, and then bent up 

 upon itself towards the right side before it termi- 

 nates in the gizzard, which is placed on the right 

 and anterior part of this dilatation. 



The experiments of Reaumur, Spallanzani, 

 and Hunter, and those of Tiedemann and 

 Gmelin, prove that the secretion of the pro- 

 ventricular or gastric glands is analogous to the 

 gastric juice in man and mammalia. 



In the majority of birds the gastric follicles 

 are simple, having no internal cells, dilated 

 fundus, or contracted neck ; but from their 

 external blind extremity proceed with an 

 uniform diameter to their internal orifice. This 

 form obtains in the zoophagous and omnivorous 

 birds. In the Dove-tribe the follicles are of 



Part of the proventriculus of a 

 Swan dissected. 



a conical shape. In the Swan they are tubuli- 

 form ; in the Goose and Turkey they present 

 internal loculi ; in the Ostrich and Rhea these 

 loculi are so developed that each gland forms 

 a racemose group of follicles, terminating by 

 a common aperture in the proventriculus. 



The subjoined figures from Home's Com- 

 parative Anatomy (vol. ii. pi. Ivi.) show the 

 different forms of the solvent or proventricular 

 glands in different birds. 



Fig. 160. 



Eagle. 



Gannet. 



Sea-gull. 



Pigeon. 



Swan. 



Goose. 



Fowl. 



Turkey. 



Rhea. 



Ostrich. 



The gastric glands are variously arranged. 



Among the Ruptores, we find them in the 

 Golden Eagle disposed in the form of a broad 

 compact belt ; in the Sparrow-Hawk this belt 

 is slightly divided into four distinct portions. 



In the Insessores the glands are generally 

 arranged in a continuous zone around the pro- 

 ventriculus; but in some of the Syndactyli, 

 as the Hornbill, the circle is composed of the 

 blending together of two large oval groups. 



Among the Scansnres the Parrots have the 

 gastric glands disposed in a continuous white 

 circle, which is at some distance from the small 

 gizzard. In the Woodpeckers the glands are 

 arranged in a triangular form, with the apex 

 towards the gizzard. In the Toucan they are 

 dispersed over the whole proventriculus, but 

 are more closely aggregated near the gizzard ; 

 the lining membrane of the cavity is reticulate, 

 and the orifices of the glands are in the inter- 

 spaces of the meshes. 



Among the Rasores the Pigeon shows its 

 affinity to the Passerine Birds in having the gas- 

 tric glands of a simple structure, and arranged 



