266 
PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
The walls of the bulla are thin and the interior is hollow and free from 
cancellous tissue. The external auditory meatus is far removed from the 
bulla and yet there is no visible connection between them and it is uncer- 
tain whether there is any tube other than that formed by the junction of 
the postglenoid and post-tympanic processes of the squamosal. The 
meatus itself is a small, irregularly circular opening, without any project- 
ing edge or lip, which has a far lower position, level with the upper part 
of the occipital condyle, than in the Santa Cruz Toxodonta or Typotheria. 
The lachrymal, the limits of which are not easy to make out in either 
of the skulls, is, to all appearance, a very small triangular bone, without 
spine, which is exposed at the supero-anterior margin of the orbit; the 
foramen is not visible from the side. 
The frontals have a decidedly curious and exceptional form and their 
appearance changes considerably with age. They are very short and 
broad and anteriorly are very deeply emarginated to receive the nasals, 
the emargination extending backward nearly or quite to the line joining 
the two postorbital processes. Behind the latter the frontals are very 
much contracted and pass into the notch formed by the divergent anterior 
ends of the parietals, but these posterior extensions are decidedly shorter 
than in Nesodon. In the young animal the postorbital processes are 
quite short and the orbits have hardly any bony roof, but in the fully 
adult skull the processes are very prominent, though not so long or so 
much decurved as in Nesodon , and the frontals are extended well out- 
ward over the orbits, thus greatly changing their appearance. The fore- 
head is very broad across the postorbital processes, narrowing anteriorly, 
and moderately convex transversely, showing the low protuberances 
caused by the frontal sinuses. There are no distinct temporal, or supra- 
orbital ridges, but in the type of H. segovice a shallow depression (which 
seems to be too symmetrical to be the result of the down crushing that 
the skull has undergone) makes the posterior part of each frontal stand out 
as a broad, flattened ridge. The anterior emargination, which lodges the 
nasals, is very deep and greatly shortens the frontals in the median line. 
The sutures with the posterior ends of the nasals form two nearly straight 
lines, which meet at an angle considerably greater than a right angle, 
though interrupted, it may be, by a very short, asymmetrical nasal pro- 
cess from one frontal only. 
The nasals are altogether different from those of the Santa Cruz Typo- 
