GILMORE: OSTEOLOGY OF BAPTANODON (MARSH) 93 
posteriorly is somewhat concave and looks outward and backward ; anteriorly it is 
somewhat rounded, sloping in toward the nasal opening. The inferior side is nearly 
straight though elevated obliquely from back to front. 
Maxillary (ma.). — The anterior half of the left maxillary of specimen (No. 603) 
was firmly fastened to a section of the left ramus by the intervening matrix and 
being separated from its position in the skull we have a splendid view of the form 
and structure of the anterior half of this bone. Laterally this element is subtri- 
angular in outline. It commences posteriorly under the anterior border of the eye, 
from which it is separated by the anterior portion of the jugal and the posterior 
branch of the lachrymal. Anteriorly it expands into facial, alveolar and palatal 
aspects, again tapering out to a slender pointed anterior end. The complete outer 
anterior view is hidden by the enclosing premaxillary. The median superior 
margin contributes a part to the lower boundary of the nasal opening. On the 
median superior surface a long slender horizontal process is developed which fits 
into a corresponding depression in the premaxillary. The matrix has not been 
removed sufficiently from the inside to determine whether it articulated with other 
bones beside the palatines and premaxillaries in that region. Nothing is known of 
the upper part of the posterior extremity of the maxillary. Anteriorly the superior 
or articulating surface is rounded, being covered with longitudinal markings. 
The inferior surface anteriorly is concave and forms the deepest portion of the 
alveolar groove. 
Premaxillary (pma.).— The premaxille are characterized as in nearly all Ichthyo- 
saurians by their great length. In B. discus the posterior termination is forked as 
in many forms of this order. The lower posterior portion enclosed the anterior 
portions of the maxillary and hides it from a lateral view. From the anterior 
boundary of the nares the suture between the nasal and premaxillary extends for- 
ward and upward to where the opposite branches become confluent and cover the 
anterior extremities of the nasals. The anterior part of the snout narrows gradually 
to the end and is composed of the premaxille alone. The tip as has been already 
explained is wanting in all of our specimens. The sides are slightly flattened but 
above are convexly rounded. The median suture is obliterated in both specimens 
although the slipping of the two halves past one another in the skull belonging to 
No. 878, see Pl. X., fig. 1, indicates that such a suture existed. The anterior half of 
the premaxillary has a longitudinal channel along the side just above the alveolar 
grooye, containing pits for the entrance of nerves to the teeth. Descending to the 
alveolar surface it will be observed that this element forms the greater portion of 
the upper jaw. ‘The inner alveolar plate of the premaxillary forms the main part 
