BIRDS. 



BIRDS. 



16B 



The following three modes by which changes in the appearance of the 

 plumage of birds are produced have been pointed out by Yarrell : 

 1, By the feather itself becoming altered in colour. 2, By the bird's 

 obtaining a certain portion of new feathers without shedding any of 

 the old ones. 3, By an entire or partial moult, in which the old 

 feathers are thrown off and new ones produced in their places. The 

 first two of these changes are observed generally in the spring, indi- 

 cating the approach of the breeding season ; the third is usually 

 partial in the spring, and entire in the autumn. The subjoined cut ia 

 explanatory of the situation of the principal parts of the plumage, 

 particularly those most conducive to flight. 



A A, Primaries ; B B, tertials ; C C, lesser coverts ; D T>, greater coverts ; 

 K K, bustard wing ; Y Y, scapulars ; G, upper tail-coverts ; II, under tail- 

 coverts ; I, tail-feathers. 



That the skin and integuments of birds perform the office of 

 emunetory organs appears not only by their moulting, but also by 

 the quantity of mealy dust separated from the skin in many birds. 

 The cockatoo, for instance, discharges a quantity of white mealy dust 

 from ita skin, particularly at pairing time, according to Blumenbach ; 

 and Bruce, in the appendix to his ' Travels,' gives an account of his 

 shooting a large bearded eagle, which, on his taking it in his hands, 

 covered him with a powder which was yellow on the breast, where 

 the feathers were of that colour, and brown on the back, where the 

 plumage was of the same hue. A heron too which he shot is 

 described as having a great quantity of blue powder on the breast 

 and back. 



The glands which secrete the oil used by birds in preening and 

 dressing their plumage are situated on the upper part of the tail. 

 Water-birds necessarily require a larger portion of this protecting 

 fluid, and accordingly we find the glands largest in that race. 

 Reaumur observes, that in that variety of the common fowl which 

 has no tail (Gallui ecaudattu) these glands are absent. 

 Digative Organs. 



The bill has a horny covering which in some degree answers the 

 purpose of teeth, and indeed it is in many instances notched so as to 

 represent them. The form of this important organ varies greatly, 

 but with evidence of the most perfect design in each varied instance, 

 according to the nature of the necessary food. Thus in birds of prey 

 it well executes the office of a dissecting-knife ; in seed-eating birds it 

 forms a pair of seed-crackers for extricating the kernel from the husk 

 which envelops it ; in the swallows and goatsuckers it is a fly-trap ; 

 in the swans, geese, and ducks it is a flattened strainer, well furnished 

 with nerves in the inside for the detection of the food remaining after 

 the water is strained by that particular operation which every one 

 must have observed a common duck perform with its bill in muddy 

 water. In the storks and herons we find it a fish-spear; and in the 

 snipes and their allies it becomes a sensitive probe, admirably adapted 

 for penetrating boggy ground, and giving notice of the presence of the 

 latent worn! or animacule. The food is transmitted from the bill 

 through the oesophagus into the stomach, which is composed of three 

 parts, namely, the crop, which is a dilatation of the oesophagus, and 

 lies just before the breast-bone ; the membranous stomach (ventricule 

 succenttirid of the French) ; and the gizzard. The first of these is 

 furnished with many mucous and salivary glands ; in the next (and 

 the structure of this may !) > ved in the gallinaceous birds) 



are a number of glandular bodies which pour out a copious 

 secretion to mingle with UM food ax it is ground down by the powerful 

 gizzard, which reaches its highest drvc'lupmi'iit in graminivorous birds. 

 Tlii* mil] i* rendered still more effective by the swallowing of small 

 hard Rtniift.H by those birds with their food, a practice which is clearly 

 instinctive, and carried sometimes to a great extent. In the museum 

 of the College of Surgeons (London) is a large glass bottle entirely filled 

 with pebbles, Ac. taken from the stomach of an ostrich. The well- 



NAT. HIST. DIV. vol. I. 



known experiments of conveying bullets beset with needles and even 

 lancets into the stomachs of graminivorous birds, with the effect of 

 the total destruction of those sharp instruments in a short period, 

 need only be referred to here ; but as Felix Plater's observations have 

 not attained quite so much celebrity we shall shortly mention them. 

 He found that an onyx swallowed by a hen was diminished one-fourth 

 in four days, and that a louis-d'or lost in this way sixteen grains of 

 its weight. 



In such birds as nourish their young from the crop the glands swell 

 very much at the hatching season, and secrete a greater quantity of 

 fluid than usual. In the pigeon, which thus feeds its young, there is 

 a spherical bag formed on each side of the oesophagus, a specimen of 

 which may be seen in the museum of the College of Surgeons. It is 

 not improbable that the banter about 'pigeon's milk" took its rise 

 from this part of the economy of the bird. 



In those birds which feed on flesh, fish, or worms, and which con- 

 sequently do not require so powerful an apparatus, the muscles of the 

 gizzard are reduced to an extreme weakness, and that organ appears 

 to make only a part of the same membranous bag with the ventricule 

 succenturi<5. 



The food being thus reduced into a sort of chyme passes through 

 the remainder of the intestinal canal, where all the nutritious parts 

 are taken into the system, and the remainder is at length expelled by 

 the cloaca, where the urinary ducts terminate and the organs of 

 generation are situated. It may be worth mentioning that the liver 

 becomes much larger in domesticated birds than in wild ones (a pro- 

 pensity which can be increased by artificial means, as the gourmand 

 who revels in his ' foies gras ' well knows), and that the gall-bladder is 

 entirely wanting in some birds, the parrot and pigeon for instance. 

 Hence no doubt the saying, " He has no more gall than a pigeon." 

 The pancreas (sweet-bread) is of considerable size in birds, but the 

 spleen is small. 



Organt of Circulation, Respiration, and Voice. 



The heart in this class is of peculiar structure. Instead of the 

 membranous valve which is present in both ventricles of the heart of 

 mammifers, and in the left ventricle in birds, the right ventricle of 

 the heart in the latter is furnished with a strong muscle which assists 

 in driving the blood with greater impetuosity from the right side of 

 the heart into the lungs ; a structure rendered necessary from the 

 want of expansion of the lungs in breathing consequent upon their 

 connection with the numerous air-cells. The lungs are small and 

 flattened, and adhere to the back of the chest in the intervals of the 

 ribs, and a considerable part of the abdomen as well as of the chest 

 is occupied by membranous air-cells with which the lungs communicate 

 by considerable apertures. In addition to these, a great portion of 

 the skeleton in most birds becomes a receptacle for air. Instead of 

 marrow the larger cylindrical bones contain air, and form large tubes, 

 interrupted only towards the ends by transverse bony fibres. The 

 broad bones present internally a reticulated bony texture, pervaded 

 by the same fluid, communicated from the lungs by small air-cells. 

 The enormous bills of the toucan and of the hornbill are supplied 

 with air from the same quarter. 



The effect of this structure in lightening the body of the bird, and 

 facilitating its motions whether in flying, swimming, or running, is 

 obvious. Where the demand is greatest (as in birds of the highest 

 and most rapid flight) the supply is largest. Thus, in the eagle, we 

 find the bony cells of great size and very numerous. The section of 

 a head of the Hornbill (Buceroi Rhinoceros}, here represented, will 

 convey some idea of the structure of thes* air-cells. 



Section of the Head of tlic Hornbill (Ducrrol Rhinoceros). 



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 bronchial, or lower 

 larynx, which contains a second rima glottidis, furnished with tense 

 membranes that perform in many birds (and especially in those which 

 are aquatic) 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 



2 H 



