HISTORY OF THE fLITOPTERNA 491 



modern horses. The nasal bones were reduced to a minimum, 

 a mere vestige of their original length, the anterior nasal 

 opening being directly over the posterior, making the nasal 

 passage vertical. Such an arrangement is an almost positive 

 proof that in life the animal had a flexible prol:)Oscis, a con- 

 clusion which is confirmed by the presence, on the top of the 

 head and behind the nasal opening, of deep pits for the attach- 

 ment of the proboscis-muscles. A very curious feature of this 

 skull was that the bones of the upper jaw, the maxillaries and 

 premaxillaries of the opposite sides, united in the median line, 

 making a long, solid, bony rostrum in front of the nasal open- 

 ing, a character not found in other land mammals. 



The neck was almost as long as in a camel and its vertebrae 

 agreed with those of the latter in the very exceptional character 

 of having the canal for the vertebral artery passing longitu- 

 dinally through the neural arch, instead of perforating the 

 transverse process. As Darwin says in the passage quoted 

 above, ''it shows a clear relation to the . . . guanaco and 

 llama," but this is founded on the postulate that such a like- 

 ness must, of necessity, imply relationship. As was shown in 

 the chapters on the Artiodactyla and Perissodactyla, it is the 

 general rule among long-necked ungulates that the odontoid 

 process of the axis assumes a spout-like shape, but "IMacrau- 

 chenia was an exception and had an odontoid which retained 

 its primitive and peg-like shape ; it was, however, relatively 

 very short and in cross-section was no longer circular, but 

 oval. This may be regarded as a step toward the assumption 

 of the spout-like form, but the extinction of the family put an 

 end to further changes in that direction. 



The body was rather short and the limbs very long, giving 

 the animal a stilted appearance, while the feet were relatively 

 short. The proportionate lengths of the different limb-seg- 

 ments was unusual ; the upper arm was short, the fore-arm 

 very long, the thigh long and the lower leg quite short. The 

 humerus was very heavy ; the ulna and radius, which were 



