THE OSTEOLOGY OF HYiENODON, 501 
1 he Milk Dentit707i. 1 he canines, and in all probability the incisors also, have 
representatives in the temporary dentition. As Wortman has suggested, the first 
premolar in botli jaws appears not to be changed. The temporary second upper 
premolar is a very simple tooth ol compressed conical shape, much elongated from 
before backward at the base, and with a cingulum on the inner side. While dp2 is 
very much like its permanent successor, ipS is unlike any of the permanent series; 
it consists of four cusps in the same fore-and-aft line, an anterioi' and two posterior 
basal cusps, with the protocone, and considerably resembles a premolar of Tcnino- 
cyon. The last milk-tooth, is constructed like “l, but the two antero-external 
cusps, corresponding in position to the para- and metacones of the molar, are of 
more nearly equal size and less closely approximated, the posterior trenchant ridge 
is less elongated, and the whole crown is lower. There is no trace of an internal 
cusp (deuterocone), though the tooth is carried on three fangs. 
Tlie lower milk dentition has been described by Wortman (No. 4, p. 226), and 
I can add little to his account. The first premolar appears to have no predecessor, 
while dp2 1 have not seen, as it is replaced at such an early stage by p2. The crown 
of dpk has a very high and acute protoconid, with a long, posterior basal expansion, 
upon which a small cusp appears. The last milk tooth, di>4, has elements corre- 
sponding to those of ml, but somewhat differently developed and not forming a 
shearing blade; the protoconid is high and conical, while the anterior and posterior 
basal cusps (para- and metaconids) are much lower and of more nearly equal size. 
In the specimen described by Wortman, which apparently is referable to H. mus- 
telinus, dpt resembles ml much more closely than in the one which forms the basis 
of the foregoing description, a skull of a small species which is of uncertain refer- 
ence. In this specimen the upper jaw contains, besides the cani nes a nd mcisors, 
the following teeth: Pi, aud “1; in the lower jaw are pi, 2, dp3,4, ml, 2. An- 
other mandible, belonging to H. cruentus has the same teeth in use. It is evident, 
however, that ml has been in use much longer than m2, and that at an early stage 
the sectorial teeth are ^ and ml, which imitates the arrangement found m the 
permanent dentition of the carnivora, though not in the temporary set, m which 
the last milk premolars operate as sectorials. 
Tlie pcraanent canines would appear to be erupted after all the premolars and 
molars are in place. At le,,st this is true of one large specimen oi a skull belon,- 
*1 Imvrimt been able to detect the change in the incisors of either jaw. 
IMie oniv otherci-eodont families whose dentition is at all similar to hat of the 
^ I /--> onfl flip Provtvcwid^. In theformei, the premo 
Hycenodontidcc are the Oxy^^tdee. ^pich is especially strong 
bars of the upper jaw i^ve e\ l ,^q,qtion of a large proto- 
