330 CLASS XVI. 



consists of seven or eiglit vertebrse vi^lncli are moveably connected 

 with each other, and, with the exception of the last, are very short. 

 The last vertebra has no cavity for the reception of the spinal 

 marrow, and presents the form of a compressed disc; it supports 

 the tail, and sometimes differs in form according to the difference of 

 sex, as in the Peacock. 



The number of pairs of ribs corresponds of course to that of the 

 vertebrae which are regarded as dorsal vertebrae. The anterior ribs 

 do not extend as far as the sternum ^ These imperfect ribs are 

 usually attached to the transverse processes alone of the vertebras, 

 whilst the rest of the ribs are attached, each by its head, to the 

 same vertebra whose transverse process receives its tubercle. The 

 connexion of these ribs with the sternum is effected not by a 

 cartilaginous but by a bony piece, so that they are composed of 

 two bones, — a vertebral piece and a sternal piece. The vertebral 

 pieces of most of the ribs (except the anterior and one or two last) 

 have at the posterior margin of their lower part a flat appendage 

 which mounts obliquely upwards and lies over the succeeding rib; 

 in some birds this process continues a separate bone. 



The sternum is very large (with the exception of the genus 

 Apteryx), and covers not only the thoracic cavity but a large part 

 of the abdominal likewise. It is convex forwards and at the upper 

 part excised on each side for the reception of the coracoid bone. In 

 the middle of the anterior surface there is a projecting bony plate 

 running longitudinally, which is absent in the Ostrich, the Casuary 

 and the genus Ajjteryx alone. 



The anterior limbs are securely connected with the sternum; 

 there are on each side two clavicles. The proper clavicle {ps fur- 

 culare) is thin and curved; it runs obliquely from the shoulder- 

 joint downwards and backwards where it meets that of the opposite 

 side, and commonly coalesces with it completely. This bone is 

 seldom attached immediately to the sternum, but is usually free, 

 and connected with it only by a ligament or by cartilage. In the 

 nocturnal birds of prey and some species of Psittacus this bone is a 

 very thin spine, and in certain species of the last genus it is wanting, 



^ Owen regards the vertebrse to which these ribs are attached as cervical, so that 

 thus the number of these would be increased by one, two, or three. On the nature of 

 Limhs, London, 1849, 8vo, p. 103. 



