LIASSTC FORMATIONS. 
57 
previously known Pterosauria, and adding such deductions as to the status and affinities 
of the order as seem legitimately to flow from the facts. 
The first distinguishing feature of Pimorphodon, or of the present liassic type of the 
genus, is the disproportionate magnitude of the head — the more strangely dispro- 
portionate, as it seems, in an animal of flight. 
The head is large in proportion to the trunk, not only in respect of length but of 
depth, and probably, also, breadth ; nevertheless, the shape and disposition of the con- 
stituent bones are such that, perhaps, no other known skull of a vertebrate is constructed 
with more economy of material — with an arrangement and connection of bones more 
completely adapted to combine lightness with strength. 
So far as the skulls of Pterosaiiria have been sufficiently entire to shoAv the shape of 
the head, no other known species resembles Bimorphodon. The cranial part is singularly 
small : the rest is mainly devoted to the formation of the large, long, and powerful 
prehensile and manducatory jaws. Among the debris of the cranial bones, in specimens 
Pis. XVII and XVIII, the mastoid (s), parts of the occipital (paroccipital, 4), the parietal (7), 
post-frontal (12), frontal (11), prefrontal (14), and nasal (15), are recognisable : the last two 
bones, however, are concerned more with the scaffolding or buttressing of the upper jaw 
than with the protection of the brain or formation of its case. Though contributing their 
shares to the otocrane, the chief developments of the paroccipital (PL XX, 4) and mastoid 
(ib. 8) relate to the muscular connections of the head with the trunk : the mastoid joins the 
postfrontal to form an upper zygoma, giving origin to part of the temporal muscles ■, it also 
affords a fixed articulation to the tympanic, and sends down a pointed process external to the 
masto-tympanic articulation. The parietals (PL XX, 7 ), confluent at the mid line, where they 
develop a low crest, swell out slightly at the temporal fossa, indicative of the size and saurian 
position of the mesencephalon. The frontal (11) is narrow and flat between the orbits, of 
which it contributes most of the upper part of the rim. This is continued by the postfrontal 
(12) behind, which sends down a long pointed process to unite with the malar (26), and a 
shorter and thicker one to join the mastoid (s). The prefrontal (14), of a triangular form, 
contributes to the upper and fore part of the orbit, and, either directly or by a connate 
lacrymal, unites with the ascending malo-maxillary process (21, 26), and the base of the pre- 
frontal articulates with the frontal and the nasal. The nasals (15), to the usual con- 
nections with the frontal, prefrontal, and medial process of the premaxillary (22'), superadd 
a union Avith the lateral ascending process of the maxillary (2l>‘), completing the bar 
between the nostril [ji] and the antorbital vacuity {a). The nasal bone forms the upper part 
of the nostril ; the rest of the boundary of that singularly wide aperture is formed by the 
premaxillary and maxillary. Of the basis cranii and palate there do not appear to be 
any recognisable parts preserved. The maxillary is overlapped by the hind alveolar part 
of the premaxillary, and unites therewith by a long oblique suture (21")- The maxil- 
lary, receding, expands and sends upward a long slender pointed process to articulate 
8 
