DR. E. EAT LANKESTER ON OKAPIA. 289 



indeed, in any mammal at all, excepting Giraffa and its extinct allies Samothenum and 

 Sivatherium (see text-fig. 9). 



The bifoliate form of the canine of the Giraffidae has no obvious explanation. The 

 existence of fissures in teeth of this shape and position finds a parallel in the curiously 

 fissured incisors of Galeopithecus. A closer point of contact is presented by the outer 

 lower incisors of Sus and Anchitherium, which have a distinct secondary lobe. The 

 canines of many Insectivora present a crown with two lobes, a feature which 

 Dr. Forsyth Major considers as pointing to the derivation of the canine from a 

 premolar. The great development of the second plate or " folia " in the Giraffe's canine 

 obviously serves the place of an additional tooth in increasing the amplitude of the 

 semicircular grip of the mouth. There is no adjacent tooth on the diastemic margin 

 of the canine to interfere with expansion in that direction, and so the accessory growth 

 has free play. If the increase of the mouth-grip was the original motive of the 

 selection resulting in a bifoliate canine in Giraffidae, it seems probable that Okajjia, 

 with its very small mouth-grip and small incisors and canines, is not in respect of its 

 front teeth so primitive as Giraffa, where both incisors and canines are of so large a 

 size (proportionately to the other teeth) that the whole group or arch of front teeth 

 may be regarded as having attained a maximum only capable of increase by the 

 addition of a lobe to the outer member of the series (the canines) on each side. 



The great size of the incisors and canines is especially striking in the young 

 Giraffe with milk-dentition and a lower jaw measuring only seven and a half inches 

 from the angle to the symphysis (see text-fig. 12, p. 293). 



I have had drawings prepared, which are here reproduced (text-fig. 9, p. 288), 

 showing (A) a lateral view, natural size, of the canines and incisors of an adult 

 Giraffe, by the side of which are represented, also of the natural size, lateral views 

 (B) of the deciduous canine of the Giraffe, (C) of the permanent canine of 0/capia, 

 (D) of the permanent canine of Samotherium, and (E) of the permanent canine of 

 Sivatherium. The extremely small size of the permanent canine of Okapia and the 

 large size of the deciduous canine of Giraffa are thus rendered very obvious. 



In our lower jaw of Okapi (PI. XXXII. fig. 12) the canine of the left side has a 

 bifoliate crown, whilst that of the right side has the crown broken and worn away. 

 They are obviously only milk-teeth, and on cutting into the jaw below that of the 

 right side we discovered, as we expected to do, the fully-developed bifoliate canine of 

 the permanent set, which is drawn in PI. XXXI. figs. 4, 5, and in the text-fig. 9, 

 p. 288. This agreement in a point of minute but definite detail, found in Giraffidaj 

 and Okapia alone, has greater significance than any of the more general points of 

 resemblance presented by the skulls. 



An important feature in the skull of Giraffa, which it is difficult to define, is one 

 which I can only speak of as " a tendency to tumescence" of the roofing-bones. This 

 feature is common to Okap'ia and Giraff'a. It is well known that in the adult Giraft'e 



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