1896.] MAMMALIAN DENTITION. 573 
very late elongation of the jaw, not to the retention of a primitive 
character. 
The Molar Teeth. 
In the younger of my two specimens m.1 alone was developed, 
while in the older stage two molars were present above and below ; 
in the latter specimen a very strong lingual development of the 
dental lamina was noticeable in relation to = that connected 
with m.1 being specially large (Plate XXV. fig. 26, d.1.), and a less 
marked but similarly related structure was observable in connec- 
tion with m. 2. 
The Cusps. 
The posterior premolars and all the molar teeth belonging to 
the upper jaw of this genus exhibit a high triangular crown 
surrounded by alow cingulum, this latter being most marked in the 
postero-internal region of the tooth (Plate XXVI. fig. 34); the 
trigon is characterized by the presence of 3 cusps, of which the 
antero-internal (5) is the dominant and is connected by an oblique 
ridge with the cusps usually regarded as the paracone and metacone 
respectively (2, 3)--this tooth apparently presenting an almost pure 
tritubercular type’. On examining ™.1 in my oldest specimen, 
this tooth was found to be composed of a prominent main cone 
slightly inclined inwards, undoubtedly the protocone of the 
adult tooth; while growing out low down from the external surface 
of this main dental germ were two smaller cones—a slightly more 
pronounced anterior one occupying the position of the future 
paracone, and a less developed postero-external cone situated well 
behind the main cone, %. ¢. the exact position of the metacone. 
The order of cusp-development is given below :— 
1. Protocone. 
2. Paracone. 
3. Metacone. \ Nearly simultaneous. 
In the deciduous 4th premolar likewise the protocone develops 
first, but here the metacone is in advance of the paracone. 
The lower molars and posterior premolar are beautiful examples 
of the trituberculo-sectorial tooth, consisting of a high trigon and 
a low slightly developed heel ; the three cusps of the trigon are 
pronounced—the protoconid (antero-external) being the largest, 
the metaconid is next in size and almost hidden by the former as 
it lies immediately internal to it, the paraconid being the smallest 
and most anterior cusp. 
The development of these cones is well seen in m.1&m.2 of my 
older specimen, and it is at once obvious that the protocunid is the 
original dentine germ, the other cusps being later outgrowths from 
1 The upper cheek-teeth of Hemicentetes should be examined by trituber- 
culists, for in this genus a coiplete transition between the triconodon 
premolars and the trituberculate molars can be seen. : 
