ESPECIALLY MYCTOPHOIDS 103 
and opens in two places on to the surface of the bone. One opening faces anteriorly, 
the other ventrally. The branch of the sensory canal which passed out through the 
anterior opening possibly continued on the lateral surface of the premaxilla where a 
distinct groove is observable. 
Hyopalatine bones. The hyomandibular is large and has an elongated head. 
The lateral face bears a crest originating on the anterior region of the head and 
passing postero-ventrally to the rear of the bone where it is joined by a further crest 
running ventrally from the posterior region of the head. The combined crest passes 
ventrally, and shallows until it disappears at the ventral extremity of the bone. The 
opercular condyle is found on the posterior edge of the hyomandibular within the 
upper half of the bone. Laterally, anterior to the crest, the hyomandibular is thin 
and covered in part by the expanded metapterygoid. The quadrate condyle is 
normally not visible from the lateral aspect since it is covered by an upgrowth of the 
articular lateral to the articular facet. The quadrate is triangular in shape, and 
indented postero-dorsally at the upper limit of the groove on the medial face which 
contained the symplectic. The pterygoid region bears a uniform series of large, 
laterally compressed, acutely pointed teeth. The palatine bone is prominent and 
tumid and attached to the anterior end of the pterygoids. Postero-dorsally the 
palatine is slung from the lateral ethmoid and antero-medially it appears to be in 
association with the mesethmoid region. The palatine bears one enlarged terminal 
tooth which is set at 90° to the axis of the bone. This tooth is larger than those of 
the ectopterygoid but of similar form. 
Dermal upper jaw. The dermal upper jaw is shown in lateral view in Text-figure 
45. It consists of two bones, the premaxilla and the maxilla. The premaxilla is 
large and in two main regions which are at an angle of go° to each other. Anteriorly 
there is a premaxillary pedicel in the same plane as the skull-roof, containing 
an elongated fenestra. The pedicels meet in the mid-line and articulate with 
the anterior edge of the mesethmoid. The second region of the premaxilla is 
lateral in position and fuses with the lateral edge of the pedicel. In the region of 
fusion between the two parts of the premaxilla there is a deep groove passing anter- 
iorly to the edge of the snout region. This groove is in a direct line with the anterior 
opening of the supraorbital sensory canal on the antero-lateral edge of the frontal. 
The postero-dorsal region of the premaxilla is overlapped laterally by the anterior 
region of the lachrymal. A ventro-lateral groove passing anteriorly to the edge of the 
snout possibly contained the most anterior region of the infraorbital sensory canal. 
The entire bone is ornamented with tubercles except in the mid-line on the pedicel. 
The premaxilla decreases in depth beneath the lachrymal and tapers posteriorly. 
The maxilla enters the gape behind the premaxilla, the margins of both bones 
forming a continuous edge to the oral border. The maxilla is fused to the premaxilla 
and the line of demarcation is difficult to define. The maxilla has no ornamentation. 
The oral border bears a marginal row of teeth continuous with those on the pre- 
maxilla. The teeth are small, evenly spaced, acutely pointed and about 25 in number. 
Mandible. The mandible is shown in lateral view in Text-figure 45. It is long 
and shallow, the depth being somewhat reduced in the symphysial region. The 
