A \ATOMY OF A BIRD. 



243 



STERNUM OF FREGILUPUS 



VARIUS. (After Mum.) 



(c!l Clavicle : (SB) Scapula : (co> 

 Coracoid ; (cs) Keel of Sternum. 



"body," and others directed forwards and backwards, so as to connect each vertebra with its neigh- 

 bours ; and lastly, a lower arch, the two halves of which are not connected below, but are converted 

 into the more or less long ribs. As these vertebrae are so small it is clear that if their spines were 

 long the free movement of the neck would be greatly impeded, and they are therefore in many cases 

 little more than projecting processes. This free movement is further greatly aided by the characters 

 of the two faces of the body (or centrum] of each vertebra ; the face of each is 

 saddle-shaped, that is to say, the anterior face is concave from side to side, 

 and convex from above downwards, while the reverse of this is seen on the 

 posterior face ; in addition to this the vertebrae are separated by a disc of 

 cartilage from one another. The region of the neck is, broadly speaking, 

 distinguished from that which succeeds it by the fact that the ribs connected 

 with its vertebrae do not reach to the sternum, or breast-bone. In all birds 

 which are capable of flight this dorsal region has its parts firmly united 

 together, and the same holds for the parts which follow, till we reach the region 

 of the tail, where the more anterior vertebrae are movable on one another, 

 so as, perhaps, to serve in aid of the steering organ formed by the rectrices, or 

 feathers (co). In all living birds the caudal vertebrae are a good deal shorter 

 than the body, but in the fossil Archcaopteryx they are longer. 



The only important point to note with regard to the ribs, is the presence 

 on some of them of backwardly directed hooked processes (up. fig. on p. 241), 

 which aid in giving firmness to the thoracic region. The number of ribs is 

 variable, but there is never a large number connected with the dorsal vertebrae, 

 as there are in some Carnivora, in Hyrax, and in the Horse. 



The fore and hind limbs are connected to the body by a series of bones, 

 which form the breast and hip girdles respectively ; with the former series is also connected that large, 

 long bone with its sharply-projecting ridge (is), which is known as the breast-bone, or sternum, and in 

 the depressions on which so much muscle is collected. This sharply-projecting ridge to the sternum, 

 which is known as the carina, or " keel" (cs), is found only in the flying birds, though here and there, as 

 in the Parrot of New Zealand (Strigops), it is very rudimentary. The lower edge of the bone is often 

 imperfect, so that, as in the fowl, there are two deep clefts on each side, or there may be but a single 

 cleft, and this again may be converted into a rounded space ; in all cases these clefts or holes are 



covered, or filled by membrane, during the 

 life of the animal. Projecting in front of 

 the sternum, and often intimately connected 

 with it, are the two clavicles (cl), which unite 

 in the middle line to form the bone of child- 

 hood's delight the furcula, or "merry- 

 thought." Above, this bone is connected 

 with two bones, one of which, ' called the 

 coracoid (c), descends on each side to fit 

 into a depression on the upper edge of the 

 sternum, while the other, known as the sca- 

 pula, or shoulder-blade (sc), is set at an 

 angle to the coracoid. The scapula has a 

 backward and downward direction ; while it 

 may be noted that among mammals the coracoid is well developed only in Echidna and Ornitho- 

 rhynchus. These two last bones form, at their point of junction, a cavity into which is fitted the 

 head of the long bone of the arm (wing). In the Ratitse, it must be observed, these two bones are 

 not set at an angle to one another, and they become more firmly united together. 



As in all the vertebrate animals except fishes, the fore-limb may be divided into three parts 

 (fig. on p. 237) upper arm, in which there is one bone, the humerus (a); fore arm, in which there are 

 two, radius (d) and ulna (c) ; and hand (E), which can again be divided into three parts, which in man 

 would be called wrist, palm, and fingers. Now, in some animals the wrist-bones may be ten in 



PELVIS OF AN ADULT FOWL, SIDE VIEW. 



(After W. K. Parker.) 



(.Reduced.) 



(iJ) Ilium; (is) Ischium ; (p&) Pubos; (<) Dorso-Iumbar vertebrae; (cd) Caudal 

 vertebrae; (am) Acetabulum. 



