254 



MUSEUM OF ANIMATED NATURE. 



[Aves. 



its shape (Fig. 1164, d) at. an opposite part of the 

 circumference. Its fibres converge, and are fixed 

 into a long round tendon (Figs. 1164 and 1165, e), 

 which passes through the loop or hem (c) of the 

 quadratus, and hence turning over the edge of the 

 broad part of the sclerotic, is continued along the 

 surface of its bell-shaped portion, where it passes 

 through several thread-like loops or pulleys which 

 keep it applied to the concavity, and round a bony 

 point which projects from the surface, and is at- 

 tached near the edge of the cornea to the edge of 

 an elastic fold (Fig. 1165, /) of the conjunctiva, 

 which is called the third eyelid, or nictitating 

 (i. e. winking) membrane. It will be easily seen by 

 the help of the figures, from this description, that 

 the effect of the simultaneous contraction of the two 

 muscles will be to draw the membrane with great 

 rapidity, making it sweep over the surface of the 

 cornea. It returns by its own elasticity with nearly 

 equal quickness. A bird may be seen to use this 

 mechanism twenty times in a minute ; in fact, as 

 often as it may be necessary to cleanse the surface 

 of the eye. The colour of the membrane is milky ; 

 and it is seen to pass from the upper and inner to 

 the outer and lower corner of the eye with the 

 speed for which the act of winking is proverbial. 



Though all birds possess a tongue, it is probable 

 that but few find enjoyment in the organ as minis- 

 tering to their taste ; and in those it is soft, thick, 

 and covered with papillae. Some of the birds of 

 prey, some of the swimmers, and the parrots gene- 

 rally, have such a tongue, and there can be no 

 doubt that these taste food of a soft or fluid nature, 

 and select that which they like best. But in general 

 the tongue is horny and stiff, and appears unsuited 

 to convey such impressions, though as an organ for 

 taking food it becomes of the highest importance. 

 In the humming-birds and other -honey-suckers it is 

 a tubular pump, and in the woodpeckers it is an 

 insect-spear. In both cases it can be protruded and 

 retracted at pleasure , and the simple but beautiful 

 machinery by which this act of volition is per- 

 formed is adapted with the most masterly fitness to 

 the motion required. Upon examining the tongue 

 of the common green woodpecker (Fig. 1166), we 

 shall find that, instead of being very long, as it is 

 erroneously supposed to be, it is really very short, 

 sharp-pointed, and horny, with barbs at its sides. 

 Behind this lies the singular tongue-bone (os 

 hyoides), slender, and with two very long legs or 

 appendages (crura). This is made up of five parts, 

 consisting of a single portion and two pairs of car- 

 tilages. Let us suppose the tongue to be at rest, 

 and then the single piece lies in a fleshy sheath, 

 capable of great extension. To this piece the first 

 pair of cartilages, which are situated at the sides of 

 the neck, are joined ; while the second pair, spring- 

 ing from these, run under the integuments com- 

 pletely over the skull, and, advancing forwards, con- 

 verge in a kind of groove, terminating generally in 

 the right side of the upper jaw. This second pair 

 by their elasticity become the springs which set the 

 whole in motion. When the organ is to be pro- 

 truded, the anterior pieces are drawn together, and 

 enter the extended sheath of the single piece ; the 

 tongue is thus elongated as it were, and the bird can 

 thrust it far forth. 



The organs of the voice in birds bear a striking 

 resemblance to certain musical wind-instruments. 

 The larynx is double, or, rather, made up of two 

 parts ; one, the proper rima glottidis, situated at the 

 upper end of the windpipe ; and the second, the 

 bronchia], or lower larynx, which contains a second 

 rima glottidis, furnished with tense membranes that 

 perform in many birds (and especially in the aqua- 

 tics) the same part as a reed does in a clarionet 

 or hautboy, while the upper rima, like the ventage 

 or hole of the instrument, gives utterance to the 

 note. 



The length of the windpipe and the structure of 

 the lower larynx vary much in different species and 

 even in the sexes, particularly among the water- 

 birds. In the domestic or dumb swan the windpipe 

 is straight ; in the male wild swan (Cygnus Bewickii) 

 the windpipe is convoluted in the hollow of the 

 breast-bone like the tube of a French horn. 



See Fig. 1167, the breast-bone, with part of the 

 keel removed to show the convolutions of the trachea 

 within ; Fig. 1 168, the point of the keel, showing the 

 opening through which the trachea enters and re- 

 turns ; Fig. 1169, part of trachea of Cygnus Bewickii ; 

 Fig. 1170, the trachea of the bittern. 



The following are the conclusions of M. Jacque- 

 min, in his paper lately read before the French 

 Academy; and though many of the facts were 

 previously known, M. Jacquemin's communication 

 must be considered as a valuable addition to this 

 part of the subject. After observing that the air 

 enters not only into the lungs and about the parietes 

 of the chest, but that it also penetrates by certain 

 openings (foramina) into eight pneumatic bags or 

 air-cells, occupying a considerable portion of the 

 pectoro-abdominal cavity, and thence into the upper I 



and lower extremities, he concludes, 1. That the 

 pneumatic bags are so situated as to be ready con- 

 ductors of the air into the more solid parts of the 

 body; and that the air, by surrounding the most 

 weighty viscera, may support the bird in flight, and 

 contribute to the facility of its motions when so 

 employed. 2. That the quantity of air thus intro- 

 duced penetrates the most internal recesses of their 

 bodies, tending to dry the marrow in the bones and 

 a portion of the fluids; a diminution of specific 

 gravity is the result, the true cause of which has 

 been, in his opinion, vainly sought in the quantity 

 alone of permeating air. 3. That in birds the 

 oxidation of the nourishing juices is not entirely 

 effected in the lungs, but is much promoted also 

 in the pneumatic bags above-mentioned, for their 

 contained air operates through the membranes upon 

 the blood-vessels and lymphatics in contact with 

 them ; a more complete and speedy oxidation is 

 the result. 4. That not only the skeleton, but all the 

 viscera are much more permeable by air in birds 

 than in any of the other vertebrated animals. 5. 

 That the air-reservoirs are not always symmetrical, 

 their shape and extent depending entirely upon the 

 form and situation of the organs among which they 

 occur ; but the supply is so modified that the total 

 quantity received into the pneumatic bags on the 

 right side of the body is equal to that which enters 

 into those on the left, and indeed without the main- 

 tenance of this condition the act of flying would be 

 impossible, and that of walking difficult. 6. That 

 no portion of a bird's structure is impervious to air ; 

 it reaches even the last joints (phalanges) of the 

 wings and feet, and the last caudal vertebrae, or 

 rump-bones. The quill of the feathers is not ex- 

 cepted, as has been sometimes asserted. 7. That 

 the air within the head has a separate circulation, 

 and does not directly communicate with the air- 

 pipes of the rest of the body. 8. That in no instance 

 does the air come into direct contact with the viscera 

 or nourishing juices, but invariably through the 

 medium of a membrane, however fine and trans- 

 parent. 9. That the volume of air which birds can 

 thus introduce into their bodies, and the force with 

 which they can expel it, offer. the only explanation 

 how so small a creature as a singing-bird (the 

 nightingale, for example) is able to utter notes so 

 powerful, and, without any apparent fatigue, to 

 warble so long and so musically. 



Fig. 1171 is a section of the head of the rhinoceros 

 hornbill, showing the extensive development of the 

 air-cells. 



Birds are either carnivorous, insectivorous, grani- 

 vorous, or omnivorous ; and their digestive apparatus 

 is modified accordingly. The crop, which is a 

 dilated sac at the termination of the gullet, leads by 

 a canal into a second enlargement, the commencing 

 portion of which is surrounded by a zone of 

 glands pouring out a solvent or gastric fluid. This 

 portion is termed ventriculus succenturiatus, and in 

 granivorous and many other birds conducts to the 

 gizzard, composed of two firm voluminous muscles, 

 surrounding a cavity lined with a thick tough mem- 

 brane. These muscles exert a sort of opposite, 

 grinding motion, with pressure on each other, like 

 two mill-stones, and the effect is a reduction of grain 

 and other vegetable matter into a pulpy mass; but 

 this cannot be done without a number of pebbles or 

 coarse particles of sand are swallowed with the food 

 (at least in granivorous birds), which by the work- 

 ing of the walls triturate the food among them. In 

 mollusk-feeding ducks the gizzard is enormously 

 powerful, grinding down hard and sharp shells. In 

 carnivorous birds there is no gizzard. 



Birds are all oviparous, that is, they produce eggs 

 which are hatched by incubation, and from which 

 the young are excluded, in different degrees of de- 

 velopment, those of the gallinaceous and duck tribes 

 being the most matured ; they are indeed capable 

 of running about and picking food in the course of 

 a few hours. Our pictorial museum contains an 

 interesting series of eggs in different stages ; but of 

 these our notice must be very cursory. 



Fig. 1172 represents the egg-organ of the fowl : 

 the eggs in this apparatus are found in all stages of 

 maturity, from a minute yellow grain, upwards, to 

 the size of a walnut ; the largest are destined to be 

 laid first ; all are enveloped in a delicate membrane, 

 but are destitute of the white, or albumen, and the 

 shell; they exhibit the germ of the future bird, 

 under a slightly elevated spot: see Fig. 1173. After 

 becoming disengaged and passing into the egg- 

 tube, they become covered with albumen, This with 

 a double membrane, and lastly with a calcareous 

 envelope. The albumen is laid on layer after layer 

 in the egg-tube, and gradually coats the membrane 

 enclosing the yolk, some of it being inspissated so as 

 to form an almost invisible membrane, the chalaza, 

 which, being twisted by the revolutions of the yolk, 

 is gathered into delicate spiral cords, retaining 

 the yolk in its place. This albumen and chalaza 

 are secreted in the first part of the egg-tube; in 

 the next part the investing membrane (membrana 



I pulaminis) is formed and added, and lastly the 

 shell. 



The anatomy of the egg, prior to the commence- 

 ment of incubation, says Professor Jones, is suffi- 

 ciently simple (see Fig. 1174). Immediately be- 

 neath the shell (permeable by air) is the membrana 

 putaminis, consisting of two layers, separating at 

 the_ larger end, so as to leave a space called the 

 vesicula aeris, which is filled with air containing 

 an unusual portion of oxygen, destined to serve for 

 the respiration of the future chick. Enclosed in 

 the membrana putaminis is the albumen with the 

 suspending cords (chalaza), and lastly the yolk with 

 its germ, enclosed in the membrana vitelli. It is 

 by the natural warmth of the body of the parent^ 

 brooding over the eggs, that the vital, though as 

 yet torpid, germ is called into activity, and begins 

 to develop. Its progress is gradual, but rapid, till 

 the chick breaks from its imprisonment, and com- 

 mences a new career. 



The changes which the chick undergoes in the 

 egg during the process of incubation have engaged 

 the attention of many philosophical naturalists, 

 who have given the minute details of every phase : 

 we shall not follow them, but refer to the series 

 in our pictorial museum, as exhibiting the progress 

 with sufficient clearness for those to whom minute 

 anatomical disquisitions (scarcely allowable under 

 our present plan) would not prove very attractive. 



Fig. 1175, an egg as it appears twelve hours after 

 incubation, with a magnified view of the germ in 

 its first stage of development. Fig. 1176, an egg 

 as it appears sixteen hours after incubation, with 

 a magnified view of the embryo chick. Fig. 1177, 

 the same, thirty-six hours after incubation. Fig. 

 1178, the same, with the chick and the first ap- 

 pearance of the principal blood-vessels magnified. 

 Fig. 1179, an egg opened four days after incuba- 

 tion, with a magnified view of the chick. Here the 

 pupil of the eye is distinctly visible, and in the 

 head are five vesicles, filled with a fluid ; and these, 

 as they enlarge, approach each other, coalesce, and 

 form the brain invested with its membranes. Fig. 

 1180, the appearances of the fifth day: the lungs 

 now begin to form. Fig. 1181, the egg and mag- 

 nified chick six days after incubation. "The spinal 

 marrow, divided into two parts, is extended along 

 the trunk. Fig. 1182, the appearances seven days 

 after incubation. Fig. 1183, the development eight 

 days after incubation. Fig. 1184, the same, nine 

 days after incubation. Fig. 11S5, the same egg turn- 

 ed more to its right side. The bones are now begin- 

 ning to form. Fig. 1186, tenth day. The muscles, 

 of the wings and germs of the feathers appear. 

 Fig. 1187 represents the chick at this stage re- 

 moved from the egg. Fig. 1188, the fourteenth day. 

 Fig. 1189 shows the external half of the vesicle re- 

 moved; Fig. 1190, the chick removed. Fig. 1191, 

 the eighteenth day. Fig. 1192, the same, with part 

 of the vesicle removed, showing the chick more 

 clearly. Fig. 1193, the chick opened to show the 

 absorption of the yolk into the body. Fig. 1194, 

 the condition of the chick on the "twentieth day. 

 Figs. 1195 and 1196, the position of the chick in 

 the egg previous to liberation. Fig. 1197, eggs 

 fractured by thejncluded chicks in the act of libe- 

 rating themselves. Fig. 1198, positions of the 

 shell after the escape of the chick. Contrary to 

 what some persons suppose, the chick frees itself 

 from its narrow prison by its own exertions, and not 

 by the aid of the mother, as some have supposed 

 from the circumstance that pieces of the shell are 

 often broken off', while the membrane within re- 

 mains unruptured : but the fact is that the mem- 

 brane is yielding and elastic, while the shell is not ; 

 the latter therefore breaks, while the membrane 

 stretches. It might be supposed that this task was 

 much above the streugth of the yet feeble chick, 

 did we not reflect that instinct calls upon it to 

 exert its utmost energies, and that its very position 

 favours its efforts. The bill is still sol't, indeed., 

 and might at first seem ill fitted for breaking the 

 shell ; but a provision is made — for, as Mr. Yaneil 

 observes, " upon the curved part of the upper man- 

 dible, just above the point, will be seen a small 

 horny scale, nearly circular, having at its centre 

 a hard and sharp projecting point, and, by the 

 particular position of the head, this sharp point is 

 brought into constant contact with the inner sur- 

 face of the shell." Such, at least, is the use gene- 

 rally attributed to this horny point; and it is to be 

 remarked that when the chick escapes, and the 

 beak hardens by exposure to the air, it soon falls 

 off, and on the" second or third day only a light- 

 coloured mark is observable on the spot it had oc- 

 cupied. In pigeons, and other birds which are long 

 before they become capable of running about and 

 feeding themselves, this horny point remains for 

 more than a week. It is worthy of note that on the 

 beak of the very young Ornithorhynchus a similar 

 homy scale exists. Here, then, we leave our pre- 

 liminary observations, and advance to our pictorial 

 specimens of the feathered tribes. 



