No. 2.] THE HARD PARTS OF THE MAMMALIA. 209 
joint. This was clearly for the reason that movements of the 
vertebral column were not necessary for locomotion, which was 
performed by the aid of stout limbs, on land. 
B. The Relative Lengths of the Vertebre. 
The extreme abbreviation of the cervical vertebrz in the 
Cetacea has been already referred to, and a cause suggested. 
Tais is the disuse naturally following increased power of turn- 
ing che body about in the medium in which they live. As a 
matter of fact the inverse relation between the two functions 
may be observed in many marine Vertebrata. Such are fishes 
in general, marine turtles, and Ichthyosauri. A few fishes 
(Dercetidz) and the Plesiosauri had long necks, but these 
animals may be supposed to have used their necks in exploring 
holes in reefs or the shores and bottom of the ocean. 
Great elongation of the tail and neck is found in certain types ; 
the former especially in some Edentata (Manis) and Rodentia, 
and the latter in Artiodactyla. Length of tail may be regarded 
as an inheritance from, or reversion to, Reptilian ancestors ; 
but length of neck is a direct adaptation to the habits of the 
animal, and is always correlated with length of the fore legs. 
In animals which take their food from the ground it is not diffi- 
cult to see in it a result of strains in the long direction, aided 
by gravity, as in the Hyanas and Artiodactyla; but in those 
which browse like the giraffe, the mechanical conditions are 
different. I cannot demonstrate the correctness of the view of 
Lamarck that the enormously long neck of the giraffe was 
produced by continuous stretching upwards. Muscular contrac- 
tion can only result in the straightening of che neck and 
limbs, but not in the application of any extensor energy. For 
the present we may suppose that the mere effort of straighten- 
ing the limbs and neck long continued would be equivalent to 
use and would determine nutrition to the parts. With the 
straightening would occur numerous lateral strains, which would 
conduce to the same result. 
In the Hyzenas the case is clear. The fore legs and neck are 
subjected to especial strain in their mode of feeding. After 
Canidz and Felidae have deprived a carcass of much of its 
flesh, the Hyzenas devour the skeleton and ligaments. Their 
