THE POPULAR EDUCATOR. 



purpose of maintaining warmth, and assisting in aerial pro- 

 gression. Each feather is, as Paley truly observes, a mechanical 

 wonder. When fully formed, a feather is composed of a central 

 cylinder or quill, by which it is attached to the skin ; a shaft. 

 which is the tapering continuation of the quill ; and the vane 

 or beard which projects from each side of the shaft. The latter 

 is composed of barbs and barbules. The feathers present some 

 variations in size and form in different parts of the body. They 

 4tre variously coloured, and form the chief feature of ornamental 

 beauty of birds. The feathers are formed by the conversion of 

 the cells of the outer layer of the epidermis (skin) into horn-like 

 material. 



TJie Mandible cr Bill consists of two portions, formed by the 

 elongated upper and lower maxillary bones, covered over with a 

 horny sheath, which serves the place of teeth. Besides being 

 a prehensile organ, the bill aids in the masticatory process to a 

 certain extent, and in some birds, e.g., the parrot, assists in 

 climbing, thus acting as a third foot. It presents many inte- 

 resting modifications of size and shape, from the filamentous 

 cone of the humming-bird to the hnge bill of the toucan. The 

 food, and manner of obtaining it, peculiar to each species, 

 determines the size, shape, and degree of hardness of the bill. 

 Thus it is strong and hook-like in those which tear their prey ; 

 short and conical in the grain-eaters ; probe-shapod in thoso 

 which live principally on insects. In the ibis, the bill is curved 

 down. In the jabiru (Fig. I., c.) it is bent up. It is dilated at 

 the extremity in the spoonbill. Ducks, geese, etc., have their 

 bills flattened. In some birds it is dentated. Besides these, 

 there are a variety of shapes, extremely interesting. 



The Tongue presents almost as many peculiarities as the 

 mandible, and like it serves for the most part as an organ of 

 prehension. It is composed of nriscles, covered with a horny 

 sheath, and supported by one or two bony pieces (hyoid appara- 

 tus), prolonged backwards behind the head (Fig. VIII.). This 

 byoid apparatus is very remarkable, especially in those birds 

 which dart the tongue rapidly at insects, as tho woodpecker 

 (Fig 1 . VIII.). In the latter, the tongue is armed at its tip with 

 harp-pointed processes for transfixing insects. In the fieldfare 

 ^Fig. II., 6.) the horny sheath of tho tongue terminates in fino 

 filaments. In the snipe (o) it is long and slender. It is very 

 short in the kingfisher (d). Tho tongue of the goose (c) has 

 projecting from its sides a number of recurvatei spines. Tho 

 honey-eaters have the extremity of their tongue furnished with 

 a tuft of horny, hair-like filaments. These peculiar shapes of 

 the tongue are, like the mandibles, determined by the kind of 

 food, and the method of obtaining it. Beneath the tonguo 

 there are a number of small cellular masses, called salivary 

 glands. These furnish a gucimy-like fluid (saliva), which 

 jnoistens the food. In tho woodpeckers, and other insectivora, 

 the saliva is viscid, to enable them to entrap insects. 



Alimentary Canal. The first portion of the digestive tract, 

 extending from tho mouth to the stomach, is called the gullet. 

 Its length is proportionate with the bird's neck. It is usually 

 wide, and in some birds capable of great distension. At the 

 lower part of the neck it communicates with a receiving cavity 

 or crop (Fig. III.), where the food, after swallowing, remains 

 lodged for a time. A little below tho crop thero 13 another 

 dilatation, the proventriculus, or second stomach (Fig. III., 3), 

 and below this a third, the gizzard. The crop is a temporary 

 reception-bag, the food lodging there until the gizzard is ready 

 to receive it. It is single, but of large size in the common 

 fowl (Fig. Ill,, 4). The pigeon has a double crop. In many 

 fcirda it is wanting, the food passing along the gullet to the true 

 tomach at once, or, as in some birds that swallow whole fish, the 

 gullet is distended into a pouch-like cavity, serving the pur- 

 pose of a crop. The proventriculus (Fig. III., 3) may be smaller 

 cr larger than the gizzard. Its walls are thickly studded with 

 email follicles called gastric glands, which pour out a fluid to 

 macerate the food, and to reduce it to a condition more readily 

 acted on by the gizzard. The gastric glands are variously 

 arranged, and present some differences in size and shape. Some 

 of these are shown in Fig. IV., a, 6, c, d, c. 



The gizzard, composed of a dense aggregation of muscular 

 fibres, is covered on its internal aspect by a dense skin-like mem- 

 brane, thus forming a powerful agent for the mechanical reduc- 

 tion of the food. Many birds further increase the power of reduc- 

 tion by swallowing pieces of flint, or other hard substances. 



The intestinal portion of the alimentary canal retains much 



of the simple reptilian form. It varies from twice to eight 

 times the length of the body. The first portion of the intestine, 

 immediately succeeding the stomach, is called the duodenum, 

 and is arranged in a characteristic loop-like fold, the interval 

 being occupied by a gland called the pancreas, which is similar 

 in structure to the salivary glands. The remaining portion is 

 also more or less folded, but in an irregular manner, and finally 

 terminates in a short tube of greater calibre, called the large 

 intestine. In the mammalia, the large and small intestines are 

 separated by a valvular fold of the mucous lining; in birds, 

 however, there is no such arrangement. The point of termina- 

 tion of tho one and commencement of the other is marked by 

 one or two pouches called caeca (Fig. III., 6), one on each side o" 

 the intestine. They vary in length from a simple offset, as in 

 the Soland goose, to processes three feet in length, as in the 

 grouse. The interior of the caeca of the ostrich is arranged in 

 a spiral manner. The c3ca are wanting in many birds, as the 

 cormorant, wryneck, toucan, some vultures, etc. The large in- 

 testine is short, straight, and destitute of folds, and terminates 

 in the cloaca (Fig. III., 10). There is an appendage (Fig. III., 

 11) connected with the small intestine, the remains of the duct of 

 communication between tho yolk-bag and intestine in the chick. 

 Birds have no diaphragm or partition-muscle separating the 

 thorax from the abdomen ; consequently, the liver, which is large 

 and two-lobed, occupies a part of both cavities. It has appended 

 to it a gall-bladder and a bile-duct. The latter opens into the 

 first part of the small intestine, and the fluid which it conducts 

 plays an important part in the digestive process. The spleen 

 is small. The kidneys are large, and lodged along the upper 

 part of the pelvis. From each kidney a tube the ureter (Fig. 

 III., 8) passes downwards, terminating in the cloaca. Birds 

 have no urinary bladder, the urine being voided along with the 

 excrements. 



The Respiratory Apparatus. This consists of an air-tube (the 

 trachea), with an upper and lower larynx, two lungs, and a 

 number of air-sacs variously disposed throughout the body. 

 The trachea, or wind-pipe, is a cylindrical tube, composed of 

 a number of cartilaginous rings connected together by fibrous 

 membranes. Its length accords with that of the neck of the 

 bird. It is surmounted above, and also below, by a larynx. 

 The upper larynx is homologous in position, and in some respects 

 in structure, with the mammalian larynx. But not in function. 

 The lower one is the true larynx, from whence emanate the 

 sweet songs by which the feathered tribe relieve the monotonous 

 stillness of country life. 



The rings which enter into the formation of the air-tube are 

 not invariably of a uniform diameter, but sometimes present 

 eccentric arrangements, as in the turkey, heron, eagle, etc., 

 increasing in size from above downwards. Sometimes the 

 windpipe is found of a fusiform shape, thicker in the centre 

 than at tho extremities ; or it may be convoluted at the root of 

 tho neck. Sometimes one or more chamber-like dilatations are 

 found developed upon it. 



The lower and true larynx is situated upon the inferior 

 extremity of the trachea, just before its bifurcation into tho 

 bronchi. This complex apparatus will be best understood by a 

 reference to Fig. VII., a, b (after Milne-Edwards). It may bo 

 compared to a kind of osseous drum, the interior of which is 

 divided inferiorly by a traversing beam of the same nature, 

 surmounted by a thin semi-lunar membrane (Fig. VII., b, 2). 

 This drum communicates inferiorly with two apertures of the 

 glottis (rimoB glottidis), formed by the termination of the bronchi, 

 and each provided with two lips, or vocal cords. Finally, muscles, 

 whose numbers vary with the species, extend between the dif- 

 ferent rings of which these parts are composed, and move them 

 so as to stretch more or less strongly the membranes they sup- 

 port. In birds which do not modulate the sounds, the mem- 

 branous septum is wanting. In those which do not sing there 

 are no muscles proper to the inferior larynx (Milne-Ed wards), i 

 The lungs are small and undivided. A subdivision of tho 

 trachea (bronchus) enters the inner and lateral aspect of each 

 lung, and after traversing the lung by smaller subdivisions 

 (Fig. V., aa, bb), communicates on their inferior surface, by four 

 or more pairs of orifices, with the air-sacs of the body. The 

 latter communicate with the interior of the bones. Respiration 

 is thus seen to be a very active and complicated process in birds, 

 and not confined to the lungs, but shared in by every part of the 

 body where air penetrates. 



