134 COMPARISONS OF STRUCTURE IN ANIMALS, 



an instance of the former. We have akeady 

 commented upon the limbs of this animal and 

 its singular mode of life; it hangs attached to 

 the branch with the bach do-\vnwards. A long 

 neck in such an animal woidd be out of place ; 

 yet, in order that it may gaze freely, not only 

 around it on each side, and above, but also 

 survey the ground below, some provision is 

 requisite; and, accordingly, the great mobility 

 of the neck is secured by the addition of two 

 vertebrce, making nine. Mr. Bell, indeed, 

 (Trans. Zool. Soc. Part i. 1834,) regards the 

 eighth and ninth vertebrae as really belonging to 

 the dorsal series, in consequence of their having 

 a small bony appendage, considered to be a 

 rudimentary rib, attached to each, on both 

 sides. This, however, matters little ; they 

 enter into the bony structiire of the neck, 

 adding two joints more without materially 

 elongating it. Hence this animal can twist its 

 neck round and look do-wnwards, or fold it so 

 as to place the head between the arms on the 

 chest. " Mr. Burchell has observed (says Dr, 

 Buckland) that this animal can in a remarkable 

 manner, and with great facility, twist its head 

 quite round, and look in the face of a person 



