342 PATAGONIAN EXPEDITIONS! PALAEONTOLOGY. 
length of the cranium. The brain case is small in the Santa Cruz genera 
and greatly constricted postorbitally, and the orbits are placed much 
farther forward than in the Dasyuridce , opossums, or Thylacynus. In the 
latter genus (PI. LXV, fig. i), the capacity of the brain case has increased 
considerably, with a corresponding expansion of the postorbital region, 
both of which, together with the posterior shifting of the orbit, may be 
regarded as progressive characters. In the extinct members of the family 
the palate lacks the vacuities present in all existing carnivorous marsupials, 
but is perforated by a number of accessory palatine foramina. Between 
the molars, the margin of the palate is depressed into deep hemispherical 
fossae for reception of the tips of the lower teeth when the mouth is 
closed. The jugal arches are robust and rather broadly expanded, and 
the sagittal and lambdoidal crests well marked, but not very high. In the 
Santa Cruz forms, the occiput is semicircular in outline, in contrast with 
its triangular shape in the dasyures, Sarcophilus and Thylacynus. The 
lachrymal canal opens well within the orbital rim. In the majority of 
living marsupials, the opening of the lachrymal duct is placed either on 
or external to the orbital rim. Thylacynus is transitional between these 
two types of structure in that it possesses a double lachrymal perforation, 
one branch of the canal opening without and the other within the orbit. 
The number and position of the cranial foramina in the existing and 
extinct members of the family are practically the same with one important 
exception, namely, that in Thylacynus the basisphenoid is perforated by 
two large foramina, as in Didelphys (cf PI. LXV, fig. i a) whereas in the 
Patagonian forms there is but is but a single perforation. 
Borhycena and Prothylacynus resemble Sarcophilus in the fusion of the 
mandibular symphysis. In the remaining genera the symphysial union 
is ligamentous. 
2. The molars of the Santa Cruz genera are of the same type as in 
Thylacynus, differing principally in the greater reduction of M A , the loss 
of all the styloid cusps, except the antero-external, and the character of 
the heel of the last lower molar, which may be either small and conical, 
basin-shaped, or bicuspidate. The premolars are unreduced in number 
and usually increase in size posteriorly in both series. The canines are 
long, sharply pointed and slightly curved in the smaller genera. In Bor- 
hycena the fang is swollen and the point short and blunt. The incisors 
in Borhycena are reduced to f, an exceptional formula among marsupials 
