BIRDS. 497 



longitiulinal section of one of tlie cervical vertebrae 

 of the Ostrich, resembles that of an hour glass. 

 Thus a wide space is left at the junction of each 

 successive vertebra, allowing of very considerable 

 flexion, without reducing the diameter of the canal 

 beyond that of the narrow portion, and therefore 

 without producing compression of the spinal mar- 

 row. Mr. Earle found* that vertebrae united in 

 this manner may be bent backwards to a right 

 angle, and laterally to half a right angle, without 

 injury to the enclosed nervous substance. Tlie 

 design of this structure is farther evident from its 

 not existing in the dorsal and lumbar portions of 

 the spine, which admit of no motion whatever, and 

 where there is no variation in the diameter of the 

 spinal canal. 



A plan entirely different is followed in the ver- 

 tebrae of the back and loins. For the purpose of 

 ensuring the proper actions of the wings, the great 

 object here is to prevent motion, and to give all 

 possible strength and security ; and accordingly 

 the whole of this portion of the spine, together witli 

 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 the bodies of the 

 dorsal vertebrae are immoveably soldered together 

 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 



* In the paper already quoted, p. 278, 

 VOL. I. K R 



