PIGEON. 29 



Atlas is an oval ring-like bone, and the transverse ligament, 

 which is sometimes ossified, divides its aperture into two 



the upper, or posterior one, enclosing the spinal cord — 

 and the lower, or anterior one, the odontoid process of the 

 axis, which in reality represents the body of the atlas, as its- 

 development shews. 



The anterior articular surfaces of the remaining cervical 

 vertebrae are slightly concave from above downwards, and 

 convex from side to side ; while the posterior articular surfaces 

 are saddle-shaped, convex from above downwards, and concave 

 from side to side. So in a horizontal section, the centra 

 would appear opisthoccelous, while in a vertical section — 

 procoelous. 



This is a well marked character of all birds. The several 

 arches have prominent pre and post-hysapophyses. 



DORSAL VERTEBRAE 



Are seven in number, the posterior five being anchylosed to one 

 another. They may be known by their possessing ribs, and being 

 shorter than most of the cervical, but with broader neural arches, 

 in consequence of the greater development of the tranverse 

 processes. 



From some of the centra of these vertebras inferior processes,, 

 hypapophyses, are prolonged downwards, to allow of greater space 

 for the origin of the muscles which depress the neck, viz., 

 lougus colli, and recti antici muscles. The centra have cylindrical 

 articular faces, like those of the neck; 



The spinous processes are well developed. It is a character of 

 the dorsal vertebras that they have a small process on the body 

 of the vertebra for the head of the rib, while from the upper 

 part of the neural arch springs a more lengthened tranverse process 

 for the tubercle of the rib. 



LUMBAR VERTEBRAE. 



All are anchylosed, with the sacral to form a bone, which is 

 ordinarily known as the sacrum, to the transverse processes of 

 which the iliac bones are attached. • 



The first has a broad transverse process, which represents the 

 tubercular transverse process of the last dorsal. In all the 

 succeeding lumbar vertebrae this process is prolonged downwards, 

 and in the last, it springs from the centrum and neural arch of 

 the vertebra and constitutes a broad process, which abuts against 

 the ilium. 



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