100 
POSSIL REPTILIA OE THE 
undei’lapping extension of the palatal process of the premaxillary (22), which reaches to 
the palato-naris. 
The maxillary (PI. XXIV, fig. 1 , 21) begins behind, parallel with the anterior third 
of the orbit, from which it is divided by the slender fore part of the malar (26). As it 
advances the maxillary expands into a facial, an alveolar, and a palatal plate, articulating 
mesially with the ectopterygoid (PI. XXV, fig. 1 , 25), and, in advance of the palato-naris, 
with the premaxillary (22). The palato-alveolar part of the maxillary is divided from 
the facial part by the outer alveolar wall. The facial part (PI. XXIV, fig. 1, 21), coming 
into view beneath the fore part of the malar (26), expands slightly to unite with the 
lacrymal (13), and, in the species affording the subject of fig. 1 , PL XXIV, it contributes 
the middle third of the lower border of the nostril ; but, as a rule, it is separated there- 
from by the junction of the lacrymal (73) with the premaxillary (22), as in fig. 2 . ■ In 
advance of this the maxillary is overlapped by the premaxillary, which conceals it from 
view at about the fifteenth tooth, counting forward, in Ichthyosaurus tenuirostris. In no 
species does it support more than about one third of the series of teeth on its own side 
of the upper jaw. 
The premaxillary (Pis. XXIII — XXV, XXIX, figs. 1 , 22) is characterised by its great 
relative length. Its facial part begins behind by an expanded bifurcation bounding 
anteriorly the nostril ; in advance of which the bone gradually expands, overlapping 
the nasal and maxillary, descending to the alveolar border to form the major part 
of the upper jaw, and narrowing to the end. The palatal portion (PI. XXV, fig. 1 , 22), 
long and narrow, is continued backward between the maxillary and palatine to terminate 
in a point penetrating the palato-naris {p n)- 
The pterygoid (Pis. XXV, XXVI, fig, 1 , 24) is also a bone of considerable size, 
especially length. It begins behind by a triradiate expansion ; the outer short subquadrate 
branch abuts against the tympanic (28) ; the upper narrower pointed ray is wedged 
between the paroccipital ( 4 ), mastoid ( 8 ), and tympanic ( 28 ) ; the inner and longest branch is 
broad, wedged between the paroccipital and basisphenoid, reaching with its blunt-pointed 
end the basioccipital. In advance of this triradiate expanse the pterygoid contracts, pre- 
senting a concave inner border, articulating with the side of the basisphenoid (5), and a 
more concave outer border, which forms the inner one of the cavity which was occupied 
by the gristly petrosal. As it continues to advance, the pterygoid again expands, its 
outer border forming an angular process, to the fore part of which the ectopterygoid (25) 
unites; the pterygoid then extends forward and gradually inward (mesiad), decreasing in 
breadth, and is continued as a long and narrow strip of bone in contiguity with its 
fellow, bounding anteriorly the long interpterygoid vacuity («), articulating outwardly for 
one half of its extent with the ectopterygoid, and for the other half with the palatine. 
The ectopterygoid (PI. XXV, fig. 1 , 25) is an elongate plate of bone, though less 
than half the length of the pterygoid ; its rounded hind end and much of its mesial 
margin articulate with the pterygoid, the rest with the palatine, with which it combines 
