B I R 



425 



B I R 



(Skeleton of Sparrow Hawk.] 



A, Cranium, or skull. 



B, Cervical vertebra*. 



(', Thfl dotted lines indicate the extent of the anchylosed vertebras of the 

 back. 



l>. The caudal vertebr ; the letter is placed on the ploughshare, or rump- 

 bone. 



K. Ribs. 



F, Sternum, or breast-bone. 



G, Furcula, or merry- thought. 



H, II. Clavicular, or cor.-icoid bone.i > ._ ., . ., 

 IIV Scapula, or ihoulder.blade. J P n to i ' e ^desman. 



I, Humerus, or bone of the arm. 



. K, Ulna, \ Bonus of the forearm : on the ulna is the placo of insertion 

 L, Radius, J of the secondary quills. 



M, Mctacarpal bones, part of the haud winch carries the primary quills. 

 N, Phalanges of the lingers. 



(I. Ilium, ) 

 P, Pubis, > 

 Q, Ischiura, j 



Bones of the pelvis. 



, 



R, Femur, or lliigh-bonc. 



o, o. Patella, or knee-pan* 



8, Tibia and fibula, or leg-bones consolidated, 



T, T. Os calcis, or liefl-bone. 



V. V, Metatarsal, or shank-bones. 



W, W, Toes. 



Wing-bones in detail. 



G, Outline of part of furcula. !!*, Outline of part of scapula. I, Humerus, 

 or bone of the arm. K, Ulna; L, Itadius, bones of the fore-arm: on the 



ulna are the marks of insertion of the secondary quills. * *, Carpal bones, or 

 wrist. M, M, Metacarpal bones. M*, Thumb. N, N, N, Phalanges of the 

 fingers. 



' The stork, and some others of the grallee (waders),' says 

 Macartney, ' which sleep standing on one foot, possess a 

 curious mechanism for preserving the leg in a state of ex- 

 tension, without any, or, at least, with little muscular effort. 

 There arises from the fore-part of the head of the metatarsal 

 bone a round eminence, which passes up between the pro- 

 jections of the pulley, on the anterior part of the end of the 

 tibia. This eminence affords a sufficient degree of resist- 

 ance to the flexion of the leg to counteract the effect of the 

 oscillations of the body, and would prove an insurmountable 

 obstruction to the motion of the joint if there were not a 

 socket within the upper part of the pulley of the tibia to re- 

 ceive it when the leg is in the bent position. The lower 

 edge of the socket is prominent and sharp, and presents a 

 sort of barrier to the admission of the eminence that re* 

 quires a voluntary muscular exertion of the bird to over- 

 come, which being accomplished, it slips in with some 

 force like the end of a dislocated bone.' 



Muscles of Motion and External Integuments. 



We will now briefly examine the means by which the 

 framework which we have attempted to describe is set in 

 motion. ' The muscles,' writes Blumenbach, ' in this class 

 are distinguished by possessing a comparatively weak 

 irritable power, which is soon lost after death ; and by their 

 tendons becoming ossified as the animal grows old, particu- 

 larly in the extremities, but sometimes also in the trunk.' 



The pectoral muscles, as we might expect from the form 

 of the sternum, exhibit, generally speaking, the greatest 

 development. They are three in number, taking their rise 

 chiefly from the ample breast-bone, and all being brought 

 to bear on the head of the arm (humerus). Of these, the 

 first, or great pectoral, is said, as a general proposition, to 

 weigh more than all the other muscles put together. Rising 

 from the keel or crest of the breast-bone, the merry-thought, 

 and last ribs, it is inserted in that rough linear elevation 

 which may be observed on the bone of the arm of most 

 birds. This bone it strongly depresses, and so produces the 

 rapid and powerful motions of the wing, which, acting on the 

 surrounding air, carries the bird forward in its flight. As an 

 antagonist to the great pectoral muscle, the middle pectoral, 

 which lies under it, and whose office it is to elevate the 

 wing, puts forth its tendon over the point where the merry- 

 thought is joined to the clavicle and shoulder-blade. This 

 point of junction acts as a pulley for the tendon which is 

 inserted in the upper part of the bone of the arm ; and by 

 this contrivance the elevating power is situated on the lower 

 surface of the body. The third, or small pectoral, aids the 

 great pectoral in depressing the wing. Thus some birds 

 are enabled to dart away with the rapidity of an arrow, 

 while others soar to a height invisible to the gaze of man. 



We have already seen that the pelvis is prolonged back- 

 wards to a considerable extent. This formation furnishes 

 room for the attachment of the muscles which set the pos- 

 terior extremities in motion, and enables them to perform 

 the functions of walking, hopping, swimming, climbing, 

 and perching. To this end there are a set of muscles 

 which go from the pelvis to the toes. One of the flexor, or 

 bending, tendons given off from a muscle which comes 

 from the bone of the pubis runs in front of the knee, and all 

 the flexors go behind the heel, so that the mere weight of 

 the bird will bend the toes. Any one may satisfy himself 

 that this operation is purely mechanical, and not the result 

 of muscular action, by making the experiment on a dead 

 bird ; when he will find that the flexion of the knee and 

 heel will at once bend the toes. This admirable con- 

 trivance, useful as it generally is, shows itself in the most 

 striking manner when brought to bear on the limbs of those 

 birds which roost in trees. When all the voluntary powers 

 are suspended, such a bird enjoys the most profound repose, 

 and the most secure position on its perch, without an effort. 

 Avoiding a minute detail of the muscles which move the 

 jaws, of those which give that complete flexibility of neck 

 so necessary to this class, or of those which regulate the 

 movement of the tail, it will be sufficient to observe that 

 their adaptation to the functions required is most beautiful 

 and perfect. 



The integuments of birds are composed of the same parts 

 as those of the mammifers, with the addition of feathers, 

 the peculiar covering common to the whole class. The 

 beak is covered with horn, and at its base, as in the birds of 



NO. 258. 



[THE PENNY CYCLOPEDIA.] 



VOL. IV.-3 I 



