UNGULATA. 55' 



phinidcB. The other fresh-water form is the Inia Boliviensis, 

 which inhabits the rivers of Bolivia, and is found at a distance 

 of more than two thousand miles from the sea. In its essential 

 characters it differs little from its marine brethren, and it 

 attains a length of from seven (female) to fourteen feet (male). 

 The last of the Delphinidm is the extraordinary Narwhal or 

 Sea-unicom (Motiodon monoceros). The Narwhal is an inhabi- 

 tant of the Arctic seas, and attains a length of as much as 

 fifteen feet, counting in the body alone. The dentition, how- 

 ever, is what constitutes the great peculiarity of the Narwhal. 

 The lower jaw is altogether destitute of teeth, and the upper 

 jaw in the females also exhibits no teeth externally, as a general 

 rule at any rate, though there are two rudimentary incisors 

 which do not cut the gum. In. the males, the lower jaw is 

 likewise edentulous, but the upper jaw is furnished with two 

 molar teeth concealed in the gum, and with twe incisors. Of 

 these two upper incisors, that of the right side is generally 

 rudimentary, and is concealed from view. The left upper 

 incisor, on the other hand, is developed from a permanent 

 pulp, and grows to an enormous size, continuing to increase 

 in length, throughout the life of the animal. It forms a tusk of 

 from eight to ten feet in length, and it has its entire surface 

 spirally twisted.' As an abnormality, both the upper incisors 

 may be developed in this way so as to form projecting tusks ; 

 and it is stated that the tusk is occasionally present in the 

 female. The function of this extraordinary tooth is doubtless 

 offensive. 



CHAPTER LXXVII. 

 UNGULATA. 



Order VI. Ungulata. — The order of the UnguMa, or Hoofed 

 Quadrupeds, is one of the largest and most important of all the 

 divisions of the Mammalia. It comprises three entire old orders 

 — namely, the Pachydermata, Solidungula, and Ruminantia. 



The first of these old divisions^that of the Pachydermata — 

 included the Elephants, Rhinoceros, Hippopotamus, Tapirs, 

 and the Pigs; all characterised, as the name implies, by their 

 thick integuments. The name is still used to express this fact, 

 though the order is now abandoned, and is merged with tliat 

 of the Ungulata; the Elephants alone being removed to a 

 separate order under the name of Proboscidea. 



