Br. H. Woodward — On Wingless Birds. 309 



The absence of marrow in many of the bones, and its replacement 

 by air-cells, also gives great lightness to the bird's skeleton. 



Peculiarities of Vertebral Column in Birds. — The cervical region 

 has seven vertebrae constantly in man and other mammalia ; but in 

 birds the neck is greatly elongated, and has from 8 to 23 vertebrse ! 

 The neck is long and flexible, and with the beak is used in place 

 of the fore-limbs and hands. The vertebrse are convex from above 

 downwards, and concave from side to side, in front ; whilst the 

 posterior surface is concave from above downwards, and convex 

 from side to side. 



The dorsal vertebrae are from 6 to 10 in number ; the anterior 

 4 or 5 are anchylosed together to give support to the wings. All 

 the vertebrae between the last dorsal and the first caudal (from 9 to 

 20) are anchylosed together to ibrm a bone which is known as the 

 sacrum. To this the iliac bones are anchylosed along the whole 

 length, giving perfect immobility to this region of the spine and 

 to the pelvis. 



Tlie Tail. — The caudal or coccygeal vertebras vary from 8 to 10 

 in number, and are moveable upon one another. The "ploughshare- 

 bone " has several anchylosed vertebrae in it. This bears the great 

 rectrices, or quills, of the tail ; but in cursorial birds, and birds that 

 do not fly, this is not developed. 



The tail in Archceopteryx consists of 20 caudal vertebrae, each joint 

 having a pair of feathers, one on each side. The tail of embryo 

 birds is many -jointed and free, and so also is the tail in the auk 

 and penguin. 



Thorax and Fore-limb (Wing). — The thorax is bounded by the 

 ribs, of which there are from 6 to 10 pairs. They articulate in front 

 to the sternal ribs or costal cartilages ossified ; these are moveably 

 articulated to the sternum, giving freedom to the respiratory move- 

 ments of the heart and lungs. 



In front is the expanded sternum, or breast-bone, which in all 

 birds that fly has a greatly developed median ridge or keel to 

 which the pectoral muscles are attached, which move the wings. 

 This keeled breast-bone or sternum is so characteristic of birds 

 of flight as to cause all those birds which possess it to be classed in 

 the division Carinat^, or keeled birds, whilst the crest is not pro- 

 duced in birds which do not fly, as, for example, the Ostrich and its 

 allies, which are consequently classed under the Ratit^, or boat- 

 breasted birds, being destitute of a keel to the sternum. At the 

 anterior angles of the sternum are fixed the two coracoids, which 

 help to form " the pectoral arch." 



The pectoral arch consists of the shoulder-blades or scapulae, the 

 collar-bones or clavicles, called also the furculum, or 'merry thought,' 

 and the coracoids, one on each side. 



The shoulder-blade or scapula has no ridge, and is a simple strap- 

 like bone. It helps to form the glenoid cavity for the humerus. 



The coracoid bones are the two strongest bones in the scapular 

 arch ; they receive the downward pull of the muscles of the wing 

 of the bird in flight. The " clavicles " (which are usually united in 



