scott: toxodonta OF THE SANTA CRUZ beds. 
139 
The premaxillaries are relatively very large ; the ascending ramus is a 
broad, thin plate, which forms an appreciable portion of the face and has a 
suture with the nasal of 4-6 cm. in length. Thus, the nasals and pre- 
maxillaries completely enclose the anterior nares and exclude the max- 
illaries. The narial opening is large, especially in dorso-ventral diam- 
eter, of cordate shape and presenting almost directly forward, though 
having a slight obliquity, due to the inclination of the ascending rami. 
The two premaxillae are in contact in quite a long median symphysis, 
but, so far as I have been able to observe, even in aged skulls, they 
are never coossified. At the antero-superior angle of this symphysis 
each bone has a blunt, rugose prominence of no great length or height, 
though together they form a conspicuous keel, which is much larger in 
Toxodon . The alveolar portion is broad and deep, to carry the great 
incisors, and the palatine processes are also large, especially in length, 
narrowing behind to triangular plates, which separate the palatine pro- 
cesses of the maxillaries. The incisive foramina, which are relatively 
very small, are completely separated from each other by the heavy spines. 
The maxillaries are very large and make up the greater part of the 
facial region ; the pre-orbital portion has great dorso-ventral depth and 
slopes upward and inward toward the median line, thus causing the 
dorsal narrowing of the face, which is so striking and characteristic a 
feature of this skull. In undistorted specimens this facial portion, above 
the alveolar process, is often quite deeply concave, especially in the 
antero-posterior direction. The alveolar portion is also very large, in 
correlation with the great size of the teeth, and forms a large mass 
beneath the orbit; posteriorly, this mass ends in a rounded, prominent 
border, which projects freely and is not continued backward by the pala- 
tines. The infraorbital canal is very short and its anterior opening is 
placed near the orbit over m-. The palatine processes of the maxillaries 
are long and rather narrow, though broadening posteriorly, and deeply 
concave, following the remarkable curvature of the grinding teeth. 
The palatines are short and take but little share in forming the bony 
palate, hardly extending to the line of m-; they are composed of two 
quite distinct portions, a broad anterior part, which forms the hindmost 
region of the bony palate, and the part which encloses the posterior nares. 
The two portions are demarcated by a very sharp constriction a little 
behind the last molars. On the sides of the posterior nares the palatines 
