210 EVOLUTION OP" MAMMALIAN MOLAR TEETH 



the protocol) e appears as a mere internal ledge growing out from the 

 base of this structure, the metacone and subsequently the hypocone 

 being similarly derived from a backward extension of the base of the 

 primitive dentinal germ." Incidentally he adds, " I have failed to find 

 any support for the concrescence theory, neither do I consider that 

 any of the evidence put forward by Rose and Kukenthal is at all 

 conclusive in its favor/' 



Order <>/' Embryonic Cusp- Development, according to WoodvarJ. 



GROUP I. GROUP II. 



(4 genera: Eriiiaceiis, Gymnura, Sorex, Talpd). (-2 genera: Centetes, Ericulus). 



With quadri- or quinque- With tritubercular upper 

 tubercular upper molars. molars. 



1. Paracone. 1. 'Protocone' ( = pa + me. Seep.24">). 



2. Metacone. 2. 'Paracone' \ , , ., 



, , T , , f< together. 



3. Protocone. 3. ' Metacone J 



4. Hypocone. 

 (5. Metaconule.) 



1. Protoconid. 1. Protocoled. 



2. Metaconid. 2 or 3. Paraconid \ , . ,, 



rr < . . , . , -i i ( together. 



o TJ i f Entoconid. 3 or 2. MetacomdJ 



3. Heel TT - , 



IHypocomd. 



4. Paraconid. 4. Hypoconid. 



As regards the adult structure of the teeth and the embryonic order 

 of development of the molar cusps, Woodward divides the Insectivora 

 into two groups, as above. 



GROUP I. Quadritubercular Molars. The first of the quadritubercular 

 types investigated is the Malayan Gymnnra, the adult molar teeth of which, 

 according to Woodward, "resemble those of the hedgehog (Ennaccus) in 

 pattern; 1 like that genus, they exhibit five cusps which are strongly 

 developed, and in the upper jaw there is a well-marked cingulum, with a 

 small anterior and posterior cusp present in addition : in the lower jaw 

 the paraconid is less developed than in Erin ace us." In the developing 

 foetus (p. 567) the second superior molar "was less developed, and here 

 the para- and metacones were the most strongly developed, while the 

 protocone was present in the form of a large antero-internal shelf [italics 

 ours], but hardly as yet developed into a distinct cusp, though the 

 hypocone and metaconule had done so." In the Shrews of the genus 

 Sorcx (op. cit., p. 570) the author also finds in a young stage that the 

 plan of the dental germ is " roughly triangular, the main and only cone 

 being situated at the anterior extremity and slightly nearer the external 

 border." From the position of this cone, and from a comparison of the 



1 [With the important exception at least in some specimens (Fig. 65, p. 118) that the 

 hypocone is less developed, and the whole tooth strongly suggests that of the tritubercular 

 to quadritubercular Eocene genus Leptictis (Figs. 60, 67). ED.] 



