140 
PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 
have unusually broad ventral surfaces and each ends behind in a promi- 
nent, everted and rugose knob, part of which is formed by the pterygoid 
process of the alisphenoid. The posterior border of the palatines is also 
very broad and is deeply impressed by the large pterygoid fossa. The 
pterygoids are narrow slips of bone, which proximally almost conceal the 
presphenoid and end distally in recurved and very prominent hamular 
processes. The posterior nares, which are entirely behind the teeth, 
form a small opening, remarkably so in proportion to the size of the skull. 
The whole posterior palatine region is highly characteristic in Nesodon 
and differs in several respects from that seen in the Santa Cruz Typo- 
theria, as figured by Sinclair. (Cf. this volume, Pis. I, fig. 3; III, fig. 3; 
V, fig. 21 ; VIII, fig. 18; X, fig. 3.) In the latter the palatines take a 
much larger share in the formation of the bony palate, to a degree which 
varies in the different genera, and the posterior nares are displaced farther 
backward by the production of the median suture between the two pala- 
tines, so that the opening presents more backward and less ventrally. 
The hard palate is thus one of the most curious features in the skull of 
Nesodon; it is broadest behind, narrowing forward to p 1 -, thence widening 
slightly to the space behind the anterior incisors (i 1 , -), and is remarkably 
concave transversely, which is chiefly due to the great prominence of the 
alveolar processes of the maxillaries and is much more strongly marked 
in the adult than in the young animal with brachyodont milk-teeth. 
The cranial foramina are, in several respects, like those of the suillines 
and also those of the Litopterna. (See Vol. VII, p. 3.) There is a large 
and conspicuous sphenorbital foramen, a small optic foramen and a large 
foramen lacerum anterius, the two latter in close juxtaposition, but no 
alisphenoid canal, foramen ovale or rotundum. There is thus no open- 
ing visible between the foramen lacerum anterius and the foramen lacerum 
medium, the latter a very large opening, which no doubt transmitted both 
the second and third branches of the trigeminal nerve, as well as the 
eustachian canal and the internal carotid canal ; there is no other carotid 
canal on the inner side of the tympanic bulla, such as occurs in the Santa 
Cruz Typotheria. The foramen lacerum posterius is likewise a large and 
irregular opening and the stylo-mastoid foramen is of unusual size. The 
glenoid foramen is a conspicuous opening between the postglenoid 
process and the mastoid portion of the periotic. The condylar foramen, 
which is rather small, is placed near the foramen lacerum posterius. 
