THE SPINAL COLUMN OF BIRDS. ] 4"9 



correct its deviations from the perpendicular; 

 or to preserve a due balance. Sir C. Bell 

 regards this as a sixth sense, " essential to the 

 exercise of the sense of touch." 



Again ; birds are clothed with plumage, and 

 employ their beaks in arranging and dressing 

 it. The length and mobility of the neck, 

 aiford them an advantage, in this respect, of 

 no trifling importance. 



It is not only the neck, in the bird, which 

 is so free and unconstrained in its actions, for 

 the head, independently of the neck, enjoys 

 the facility of turning from side to side, or 

 indeed so much round, that the position of 

 the beak is reversed, and points over the back. 

 jMany, doubtless, have observed the odd mo- 

 tions of the head Avhich the owl is in the habit 

 of making, and how frequently it will turn its 

 broad face over i-ts back, as if its neck were 

 screwed round. This freedom of the head 

 arises from its mode of union with the first 

 cervical vertebra. If wc look at the skull of 

 a bird, we shall find, on the anterior margin 

 of the great orifice which admits the exit of 

 the spinal cord, a single tubercle ; now this 

 tiibercle is received into a corresponding little 

 pit, or socket, on the upper end of the first 



