218 



NATURAL HISTORY. 



The region of the mouth is not separated from that which follows it (the pharynx) by an 

 epiglottis, which in ourselves protects the entrance into the air-passages, nor is there any uvula 

 to guard the posterior orifice of the nose by which the air reaches the throat. The succeeding por- 

 tion of the gullet (the oesophagus) is very long, as might be supposed from the length of the neck in 

 most birds, and it is very frequently either dilated at one side, or produced into a caacal pouch (crop, 

 iitgluvies), which may, or may not, be separated by a narrow connection, from the rest of the gullet, 

 and which may be divided into two compartments. This crop serves for the detention of the food, 

 which cannot have undergone any complete process of mastication, and it is here treated to a process 

 of maceration by the fluid secreted from the walls of this organ. Passing from this receptacle, 

 the food becomes subject to the action of the stomach proper, which differs, however, from our 

 ordinary conception of a stomach, as seen in man, by being divided into two distinct portions. The 

 anterior one is known as the jyroventriculus, and it is in this that the gastric juice is brought to bear 

 upon the food, and its walls are consequently thickened by a glandular layer ; the hinder division, 

 which is known as the gizzard, forms an elongated sac, with two orifices one from the proventriculus, 

 the other leading to the small intestine in its iipper portion. The characters of its walls are very 

 different in those birds which live on animal, as compared with those that live on vegetable (grains) 

 food ; in the former they are membranous and thin, but in the latter they are enormously thick and 

 very muscular. On examination, it is seen that the dark colour of the muscles is on each side of the 

 gizzard relieved by a shining spot of tendinous material, and the walls of the gizzard have conse- 

 quently been compared to a double-bellied (digastric) muscle. The internal cavity of the gizzard is 

 lined with a dense and rough coat, and is ordinarily found to contain small stones, and occasionally 

 other hard materials. These obviously take the place of the absent teeth, when the muscles of the 

 gizzard set up that (grinding or compressing) action by which the ingested seeds are broken down. The 

 wall of the gizzard may itself also act as a rasping organ, being, as it often is, provided with a firm 

 glandular layer, the secretion of which is converted into a hard lining, the structure of which has been 

 observed in some cases to be due to interlaced filaments secreted from and continuous 

 with the glands in the wall of the gizzard. 



Notwithstanding the differences in the character of the gizzard in carnivorous 

 and graminivorous birds, it has been shown by the ever-famous John Hunter that 

 carnivorous birds can be brought to live on grains, and grain-eating birds 

 on meat. 



It is interesting, further, to note, with regard to the opening into the small 

 intestine, that in a mtmber of grain- or fruit-eating birds there is no valvular 

 arrangement to detain the food in the gizzard till it is completely triturated, for it 

 is thus that many plants have their area of distribution increased, the escaped 

 seeds passing uninjured from the intestine to find, perhaps, a suitable soil in a new 

 district. In those that swallow large stones a valve is often to be observed. The 

 difference which we have already had so frequently to notice, as obtaining between 

 the carnivorous and '' vegetarian " birds, is seen to be continued into their small 

 intestine ; just as in mammals, this portion of the tract is longer in the latter than 

 in the former birds. The anterior, or duodenal portion, is always characterised by 

 forming a loop, within which lies the gland known as i\\e pancreas, and the succeeding 

 portion is, as compared with most mammals, short. A slight elevation, hardly ever 

 of any great size, may at times be observed on the course of the short intestine. 

 This represents all that remains of the duct by which the hatching bird was con- 

 nected with the yolk. The short and straight large intestine is ordinarily separated 

 KING- fr m the preceding by a caecum ; this is generally paired (in the Herons and some 

 others it is single), and varies in length ; in many cases these csecal tubes are hardly 

 more than papillae. In the Parrot, as in the "Woodpecker and some others, these 

 caeca are absent. In the desert-dwelling Ostrich (Struthio) they are said to be as 

 much as two feet long ; but in the Emu they do not exceed six inches in length. 

 The intestine ends in a cavity, which is common to it, and to the other organs that open to the 

 exteiior in this region. This cloaca (sewer) is found in reptiles also, and in one division of the 



IMGESTIVE ORGANS 

 OF THE 

 FISHER. 



(After Macgilllvray.) 



(n) Tongue ; (6, c, <J| O3sn- 

 pbafrat; (rf, e,f) 8tn- 

 nmcli : (/, g, h, i, j, k) 

 Intestine; 0,fc) Cloaca. 



