BIRDS. 3S9 



without reducing the diameter of the canal beyond that of 

 the narrow portion, and, tlierefore, without producing com- 

 pression of the spinal marrow. Mr. Earle found' that ver- 

 tebrae united in this manner may be bent backwards to a 

 right angle, and laterally to half a right angle, without inju- 

 ry to the enclosed nervous substance. The design of this 

 structure is farther evident from its not existing in the dor- 

 sal and lumbar portions of the spine, which admit of no mo- 

 tion whatever, and where there is no variation in the diame- 

 ter of the spinal canal. 



A plan entirely different is followed in the vertebrse of 

 the back and loins. For the purpose of ensuring the proper 

 actions of the wings, the great object here is to prevent mo- 

 tion, and to give all possible strength and security; and ac- 

 cordingly the whole of this portion of the spine, together 

 with the sacrum, is consolidated into one piece. All the 

 processes are largely developed, and pass obliquely from 

 one vertebra to the next, mutually locking them together: 

 and, in order most effectually to preclude the possibility of 

 any flexion, the spinous processes, and sometimes even tl:;^^ 

 bodies of the dorsal vertebrae are immoveably soldered to- 

 gether by ossific matter, so as to form one continuous bone. 



The sacrum (v, Fig. 224) consists of the union of a great 

 number of vertebrae, as many as twenty being anchylosed 

 together for this purpose; so that they form a bone of great 

 length. The coccygeal vertebrae (q) are also numerous, but 

 are compressed into a small space, and enjoy great latitude 

 of motion, being subservient to the movements of the tail. 



The ribs are numerous, and of considerable strength: they 

 send out processes, which are directed backwards, passing 

 over the next rib before they terminate, and giving very ef- 

 fectual support to the walls of the chest. The ribs are con- 

 tinued along the abdomen, and afford protection to the vis- 

 cera in that cavity; and some arise even from the sacrum, 

 and from the iliac bones. Those which are in front are 



* In the paper already quoted, p. 278. 



