1893.] The Ancylopoda, Chalicotherium and Artionyz. 125 
cess. The maxillary bones are high. All these characters are 
very similar to those in the skulls of the primitive Condy- 
larthra, such as Periptychus, Phenacodus and Meniscotheriwm. 
We should also mention many cranial features which we 
believe belong to the category of secondary adaptive modifi- 
cations; among such are the following: (1) the large curved 
cylindrical tympanic bulle, (2) the feeble character of the 
nasals, premaxillaries and anterior portion of the mandibular 
rami. The latter modifications are associated with the reduc- 
tion of the cutting teeth. Filhol has shown that the young 
individuals of Sansan have a full set of incisors, while in the 
adult the upper incisors are rudimentary or wanting. ` 
There are other secondary features of note. The condylar 
facets are prolonged forward upon the basi-occipitals. The 
posterior face of the centrum of the axis is directed upward ; 
this and the preceding features point to peculiar flexibility of 
the neck. The centrum of the axis is long and slender, the 
odontoid process is round, the spine is unusually long and 
high. 
Looking again at the limbs we observe that the radius 
covers the entire front face of the ulna and presents two dis- 
tinct fossee for the condyles of the humerus. The tibia closely 
resembles that of some of the short-limbed ungulates in its 
cnemial crest and two fosse for the femur, in its spine and dis- 
tal grooves for the double trochlea of the astragalus which 
is like that in the short-footed Aphelops. This likeness to the 
ungulates, and especially to the perissodactyls, in the form of 
the upper foot bones and of their articulations with the meta- 
podials is most striking. The calcaneum has a long tuber 
and very broad sustentaculum. The astragalus rests widely 
upon the cuboid, its tibial trochlea is very similar to that in 
the short-footed rhinoceroses. The cuboid, navicular and 
cuneiforms are, however, extremely flattened and specialized. 
The diplarthrous character of the carpus is precisely like that 
of Perissodactyla, the lunar rests upon the cuneiform and the 
scaphoid upon the magnum, while the metapodials abut later- 
ally against the unciform and magnum. 
