General Charactees.- 



-BIRDS- 



-General Characters. 



231 



chest in birds ia arranged, so as to give it the firmness 

 necessary to bear the strain throwTi upon it in the 

 action of flight, we may now proceed to the considera- 

 tion of the stmcture of the wings, and the mode in 

 which they are supported. From the articular sur- 

 faces already mentioned as existing on the anterior 

 part of the sternum, there spring two large and strong 

 bones, which are directed upwards and forwards, at the 

 same time diverging more or less from each other. 

 These are the coracoid boms, which, in the Mammalia, 

 witli the exception of the monotremata, are reduced to 

 a rudimentary condition, and anchjdosed to the upper 

 jiart of the shoulder-blade. The superior part of each 

 coracoid bone is furnished with an articular surface, 

 which assists in the formation of the shoulder joint. 

 The remamder of this socket is formed by tlie ex- 

 tremity of tlie scapiUa or shoulder-blade, which rests 

 against that of the coracoid bone. The scapula is 

 usually elongated and rather slender, and is applied 

 upon the dorsal surface of the ribs, where it lies nearly 

 parallel to the vertical column. From tlie position 

 and strength of tlie coracoid bones, they are e\'idently 

 well adapted to furnish firm points of support for the 

 wings ; but they are further assisted in tliis office by 

 the clavicles or coUai" bones, which are usually anchy- 

 losed to each other in tlie median line, so as to form a 

 single V-shaped bone called the furculum* The 

 other extremities of the clavicles are articulated to 

 tlie inner surfaces of tlie superior extremity of the 

 caracoid bones, to which they serve as supporting 

 buttresses, and thus assist materially in resisting the 

 action of the powerful muscles of the wings. The 

 bones of the wings themselves are easily recognized as 

 corresponding with those of the anterior members in 

 the Mammalia. The humerus, or arm-bone, is a long 

 cylindrical bone articulating with tlie shoulder-blade 

 and coracoid by a ball and socket joint, and presenting 

 at its lower extremity a double articular surface for the 

 reception of the two bones of the fore-arm. The latter 

 are usually longer than the humerus, cj'lindrical in 

 form, and thickened at the two extremities ; but one 

 of them — the zdna — is always much stouter than the 

 other — the radius — which is generally very slender. 

 Tlie carpal bones forming the wrist, are two in num- 

 ber, small, and rounded. They are followed by two 

 elongated metacarpal bones of imequal thickness, 

 which are completely anchylosed together at both 

 ends. At the base of these, on the outer edge, we find 

 another small bone, which is sometimes free and 

 sometimes anchylosed to the metacarpal (fig. 137). 

 This is tlie rudiment of a thumb, and gives support to 

 a few feathers, formuig what is called tlie pinion or 

 bastard-'tt'ing. The metacaqial bones are followed by 

 the phalanges, which usually represent two fingers, 

 one of which is composed of two or three jomts, the 

 other only of one. These phalanges are endowed with 

 but little mobility, so that tlie whole wing may be 

 regarded as composed of three joints, united by a more 

 or less hinge-hke articulation at the elbow and wrist. 

 r>y tliis arrangement the wing is rendered still' when 

 extended, whilst, at the same time, its diree jouits lie 



* This is the well-known merrythougM, with the ceremony 

 of breaking which most of our readers are probably acquainted. 



nearly parallel to each other when the wing is con- 

 tracted, and thus occupy a very small space. 



The structure of the hind limbs corresponds, in like 

 manner, with that of tlie same members in the Mam- 

 malia. The femur, or thigh-bone, is usually short and 

 stout, and articulates with the pelvis by a ball and 

 socket joint, the rounded head being set on, as in the 

 mammals, nearly at a right angle to tlie axis of the bone 

 (see fig. 135, Plate 36). This is foUowed by the tibia, 

 or shank-bone, usually much longer than the tliigh, 

 and accompanied by a slender fibula. This latter bone 

 is, however, commonly attached to the tibia, and 

 it always becomes gradually attenuated towards tlie 

 apex, and disappears entirely long before reaching the 

 extremity of the shank. The knee-joint is furnished 

 with a small knee-cap, or patella. The tarsus also 

 consists of a single cylindi'ical bone, often ol gi'eat 

 lengtli ; and the foot is terminated by from two to 

 four toes containing a variable number of joints. The 

 usual number of toes, especially in the most t3'pical 

 bhds, is four ; and of these one is generally du'ected 

 backwards. 



Of the muscles by which the apparatus of bones 

 just described is set in motion, we need say but little. 

 They are generally very firm, and of a deep-red 

 colour. The principal mass of the muscles is devoted 

 to the movement of the wings. These, of course, 

 vary La bulk according to the power of flight possessed 

 by the bird, and correspond with tlie development of 

 tlie sternal keel. The muscles of the tliigh and shank, 

 are also largely developed, and it is ui the hinder 

 limbs also that we find the sinews presenting most 

 distinctly those peculiarities wliich characterize them 

 in birds. They are exceedingly white and glistening, 

 and have a great tendency to become ossified. The 

 long tendons which pass down the back of the tarsus 

 from the flexor muscles of the toes, are especially 

 remarkable in these respects. They are of the greatest 

 importance to the bird in perching ; indeed, it is to 

 tliis peculiar arrangement that the bird is enabled to 

 perch. Passing over the back of the heel, like a cord 

 over a pulley, they are necessarily stretched by the 

 flexion of this joint, caused by the weight of tlie body 

 in the act of perching. They thus exercise a sort of 

 involuntary action upon the toes, causing them to grasp 

 any object witli great fimmess, and thus retaining tlie 

 bhd secm-ely in its position even during sleep. 



It is hardly necessary to say that tlie clothing of 

 the skin in these animals consists of feathers, a circum- 

 stance from which de Blainvihe proposed to name the 

 class Penniferes. It may be as wcU, however, to give 

 a few details of the nature of these tcgunientary appen- 

 dages, which, although somewhat analogous to the 

 hairs of the Mammalia, are of a far more complicated 

 structure. 



A feather ordinarily consists of two distinct portions 

 — a central shaft or stem, and a pair of webs, occupj'- 

 ing the two sides of the shaft, and composed of nimiei- 

 ous flattened fibres or barbs, closely applied to each 

 other. The basal portion of the central stem, which 

 is partially inserted into the skin, is a hollow, homy 

 tube, usually transparent, and terminating in a more or 

 less pointed or rounded extremity. The upper portion 



