360 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 4, 



jaw is short in proportion to its depth, sending up a broad and high 

 coronoid process for the adequate grasp of a large temporal muscle " 

 — seeing that all these characters are combined in an existing gliri- 

 form Lemur, which is not a carnivore. The descriptive terms applied 

 to the coronoid would be suitable for that of a Tiger or Stoat, but 

 they seem hardly applicable to the process of Plagiaulaoc, 



The author of ^Palaeontology' lays stress on the low position 

 of the condyle, and its long horizontal neck : " The condyle is placed 

 below the level of the grinding-teeth, — a character unknown in any 

 herbivorous or mixed-feeding Mammal ; it is pedunculate, as in the 

 predaceous Marsupialia; whilst the lever of the coronoid is made 

 the stronger by the condyle being carried further back than in any 

 known carnivorous animal." But it is not a little remarkable that 

 he is silent regarding the form of the condyle itself, — the most 

 important of all the mandibular characters after the teeth ; for the 

 peduncle, on which he lays weight, is, lilte the fang of a tooth, but 

 the stalk upon which the organ performing the function is borne. I 

 think it necessary therefore to call attention to the remarks on the 

 subject contained in my former paper. In the true Carnivorous type, 

 the condyle shows more or less of a cylindrical or terete surface, 

 having invariably a transverse direction, by which it is locked in the 

 glenoid cavity of the upper jaw, thus constituting a pivot like that 

 of a pair of scissors, which constrains the blades to a vertical motion. 

 In Plagiaulaoc all these conditions are reversed, the condyle being 

 convex, with its long diameter disposed subvertically ; regarded 

 endwise, it is narrow in proportion to the height, and the outhne is 

 ovate or pyriform, the broad end being uppermost. This is a form 

 which is unknown among the Carnivora, but common in the Pla- 

 cental Eodents, with the difference, however, that in the latter, the 

 condyle having to work backwards and forwards in a groove, its 

 articular surface is disposed longitudinally. In the common Norway 

 Eat, the articular surface of the condyle is partly vertical, with the 

 pyriform outline of Plagiaulax, but more compressed ; and in one of 

 the American Marmots (No. 2259, Mus. E. CoU. of Surgeons) it still 

 more closely resembles that of the fossil genus. I cite these instances, 

 to show the undercurrent of Eodent analogy which pervades the jaw 

 of Plagiaulax throughout. But a more conclusive and irresistible 

 case of correspondence can be adduced in the condyle of the Aye-Aye. 

 In the words of the celebrated French anatomist who first settled the 

 affinities of the genus, '' La forme generale de la machoire inferieure 

 de I'Aye-Aye denote une partie forte, large, ou mieux haute et tres 

 comprimee; la branche horizontale beaucoup plus longue que la 

 verticale, qui est presque dans la meme direction. Le condyle qui 

 termine cette branche verticale, dans les autres animaux, est droite 

 ici, et presque a I'extremite posterieure de toute la machoire," &c.* 

 The condyle of the Aye-Aye has the same ovate form as that of Plagi- 

 aulax, but reversed, the narrow end being uppermost (fig. 20) ; the arti- 

 cular surface is broader and somewhat flatter than in that genus, but 

 the direction of the greater axis is the same, that is, longitudinal and 

 ■**■ De Blainville, ' Osteographie : memoire svir I'Aye-Aye,' p. 19. 



