530 Dr. C. I. Forsyth Major on the 



tlie tritubercular form of molar is to be regarded as primitive, 

 or rather as the result of a process of retrogression. 



I. The Molars. 



The homologies of the cusps of tlie molars in the Insectivora 

 have already been carefully studied by Mivart nearly thirty 

 years ago *. It was shown by this author that the upper 

 molars of Potamogale to a certain extent represent a tran- 

 sitional stage between the more complicated molars, e. g. of 

 the mole, with two triangular prisms each, and the simpler 

 ones, such as those of Centetes and Ericulus, with but a single 

 prism : — " For each of these teeth [in Potamogale^ have three 

 or four very small cusps developed from the external cingu- 

 lum, a very large cusp arising from the internal cingulum, 

 and two median cusps, from each of which two slightly- 

 marked diverging ridges proceed outwards to the external 

 cingulum, forming two very narrow triangular prisms, so 

 close together that a little more approximation would reduce 

 them to a single prism, such as exists in Centetes and Soleno- 



dony He also says : — '' Potamogale shows a very 



interesting approximation of the triangular prisms, the two 

 external principal cusps still, however, remaining distinct, 

 though in close juxtaposition. In Centetes it appears as if 

 the concentration had been carried further, the two prisms 

 uniting into one, as also tlie two external principal cusps. 

 The single representative of these, however, has two small 

 prominences on its inner side. In Chrysochloris we have 

 the maximum of concentration, there being but a single 

 triangular prism, the internal angle of which represents the 

 two external principal cusps of Erinaceus and others, while 

 internal to this there is but a single prominence to represent 

 the two internal principal cusps." 



I therefore have to state that Mivart long before mvself, 

 at least so far as the Insectivora are concerned, represented 

 the complicated character of the molars as the primitive 

 condition, and maintained that the simple form had arisen 

 through concentration or fusion. 



In opposition to this it was asserted by Huxley f that the 

 form of molar seen in Centetes is the primitive one, and, as 

 is well known, this view was subsequently supported also by 

 Cope, Osborn, and Schlosser. Huxley terms the form in 

 question " least-modified," and, according to him, the form 

 of molar exhibited by all Carnivora is easily to be derived 



* Journ. Anat. aud Physiol, ii. 1868, p. 117 et seq. 

 t Proc. Zool. Soc. Loudon, 1880, pp. 283-284. 



