100 FOSSIL REPTILIA OF THE 



underlapping 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, PI. 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 »). 



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 (s), 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 (:>;>) 

 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 



