ITS DISPUTED AFFINITY. 



447 



Length of jaw from condyle to incisive border. 



From condyle to posterior edge of coronoid 



Height of jaw to summit of coronoid 



Height of ramus in front of first true molar 



Height of ramus behind tho incisor 



Height from condyle to a line dropped vertically behind 



last molar ........ 



Height from the latter point to posterior edge of incisor 



at diastema ........ 



1-25 



1-05 



•75 



From these proportions it will be seen that both in Chei- 

 romys and Plagiaulax the condyle projects behind the edge 

 of the coronoid to the excessive extent of abont one-fourth of 

 the entire length of the ramus. Professor Owen meets the 

 argument in my paper by the assertion that the condyle of 

 Plagiaulax is ' pedunculate as in the predaceous marsupials.' 

 If so, I invite him to adduce the instance, bearing in mind 

 that the question here is one of degree. The lower jaw of a 

 tio-er now before me measures 9-2 inches from the condyle to 

 the incisive border, while the projection of the articular sur- 

 face behind the fall of the coronoid does not exceed -7 of an 

 inch, or one-thirteenth of the length of the jaw. In Dasyurus 

 and Thylacinus 1 the condyle projects behind the coronoid, 

 but nothing approaching the extent seen in the Aye-Aye and 

 Plagiaulax. As regards the functional effect of the condyle 

 being carried so far back behind the edge of the coronoid, it 

 is a plain question of animal mechanics, which the author of 

 the ' PalEeontology ' thus interprets : — ' It is pedunculate, as 

 in the predaceous Marsupialia, whilst the lever of the coro- 

 noid process is made stronger by the condyle being carried 

 further back than in any known carnivorous or herbivorous 

 animal.' As I regard it, a necessary effect would be to re- 

 strict the power of separating the jaws in front, essential to 

 a predaceous animal having laniary teeth constructed to 

 pierce, retain, and kill. And we have the direct proof in the 

 Aye- Aye, that the same arrangement there is not applied to 

 a carnivorous function. 2 



doubled. But this does not interfere with 

 the ratios of proportion. Further, in 

 the Aye-Aye the posterior margin of 

 the coronoid is assumed to be continued 

 down vertically, in order to get corre- 

 sponding measurements. The dimen- 

 sions of Cheiromys are of the natural size. 

 1 In the Ursine Dasyurns (No. 1900, 

 Mus. E. Coll. of Surgeons) the length 

 of the lower jaw is 4-2 inches, and the 

 projection of the articular surface be- 

 hind the deepest part of the sigmoid 

 notch - 4 inch, or about one-tenth of tho 



entire length of the jaw. In Thylacinus 

 (No. 1903a of the same collection) tho 

 projection of the condyle is about one- 

 eighth of the length of the jaw. But in 

 both these forms the posterior edge of 

 the apex of the coronoid overhangs tho 

 condyle; while both in PI, Becklesii and 

 the Aye-Aye the articular surface of the 

 condyle is removed about one-fourth of 

 the length of the jaw behind the fall of 

 the coronoid. 



2 In the typical Carnivora the ful- 

 crum is a fixed point, the form of the 



