86 MOSTLY MAMMALS 
Strange as are the foregoing creatures, they are exceeded 
in this respect by the long-necked and long-limbed animal 
named Macrauchenia (on account of the elongation of the 
vertebrae of the neck), specimens of which were first 
brought back by Darwin from the superficial deposits of 
Patagonia. In general form the macrauchenia somewhat 
recalls a camel; and it is a curious circumstance that, in 
common with that animal and its allies, it differs from all 
other ungulates, with the exception of certain kindred 
Argentine forms, in that the arteries of the neck pierce 
the sides of the vertebrae to take a course within the 
spinal canal, instead of passing merely through a loop of 
bone on the exterior. This remarkable resemblance is not, 
however, indicative of any affinity between the two animals, 
since, if we look at the feet of the macrauchenia, we shall 
find that they are of the odd-toed type, and each furnished 
with three digits. Moreover, the huckle-bone has the 
pulley-like upper surface characterising the odd-toed ungu- 
lates; and as the teeth approximate to those of the latter, 
we might be inclined to place the creature in that group. 
The wrist- and ankle-joints are, however, formed on the 
linear plan, and exhibit certain other departures from the 
odd-toed type, and it is therefore evident that the macrau- 
chenia and its allies constitute a third group of extinct 
ungulates peculiar to South America. Although it is by 
foot-structure that the macrauchenia is separated from all 
other members of the order, its most remarkable peculiarity 
is to be found in the structure of its skull. In an ordinary 
mammal the aperture of the nose is situated quite at the 
anterior extremity of the skull. In the macrauchenia, on 
the other hand, this aperture forms an egg-shaped vacuity 
in the forehead, almost between the eyes. Some approxi- 
mation to this remarkable arrangement is presented by 
