LIASSIC FORMATIONS. 
47 
the sacrum and contiguous vertebrse is figured in PI. XIX, fig. 2 ; and the constituent 
bones are rightly recognised by Bucldand (op. cit., p. 222). 
It is interesting to note, that the pelvis of Plerosanria, so determined, resembles more 
closely that of the existing representatives of the section of Meptilia with the 4-chambered 
heart and double-jointed ribs, viz., Crocodilia, than it does the pelvis in CUelonia and 
Lacertia. The ischium in Crocodilia, e. g., surpasses the pubis in size, and excludes that 
hsemapophysis from the acetabulum. ^ The ischium seems to contribute the larger share 
of the acetabulum in Dimorjjhodon, PI. XVIII, a- In Birds, as in Lizards, the pubis 
forms part of the acetabular cavity.® 
In the specimen, PI. XVIII, a portion, cd, of a long tail, of which the vertebrm were 
surrounded by numerous slender bone-tendons, extends backward and downward beyond 
the pelvis : a better preserved portion with three caudal vertebrge (c d') is preserved in a 
detached part of the matrix found in the vicinity of the larger slab. But to this part of 
the vertebral column I shall return in describing the more perfect specimen of the tail of 
Dimorphodon, from another individual (PL XIX, fig. 4). 
Behind the skull are four cervical vertebrm (PI. XVIII, c), and part of a fifth in natural 
juxtaposition, or perhaps a little separated at the articular surfaces. The under surface of 
the centrums and articular processes of the neural arches are exposed. The sides of the 
centrums show a slight concavity, but their crushed state obscures the natural contour of 
the under surface. The hind part of the under surface, in the last two of these 
vertebrae, shows a pair of low obtuse processes, with an indication of a convex terminal 
articular surface. The centrum expands in breadth as it advances, and sends out a short 
thick process (parapophysis) from each side of the fore part ; to which, in the last three 
vertebrae, are indications of attachment, or parts, of a backwardly produced styliforni rib. 
At the midline of the fore part of the last two of these vertebrae a fracture indicates a 
ridge or process there to have been broken off. The pre-zygapophyses are thick, and project 
far in advance of the concave anterior articular surface of the centrum : the convex 
posterior articular surface of the centrum projects as far beyond the post-zygapophyses. 
Their joints are more vertical than horizontal : the posterior surfaces looking slightly 
outward and downward. 
The superior breadth of the neural arch, as compared with that of the centrum, 
brings its articular processes into view, along each side of the vertebral bodies, in the 
degree shown in PI. XVIII, c. The character of the articulations indicate less extent and 
freedom of movement of the cervical vertebrae than in Birds, and more restriction in the 
lateral than in the vertical directions. The interlocking joints resulting from the different 
lengths of the fore and hind articular processes add strength to the part of the spine 
supporting the head. 
The cervical vertebrae of I)imorphodo7i, so far as their structure is exemplified in the 
1 ‘Anatomy of Vertebrates,’ vol. v, p. 188, fig. 119. 
2 Ib., p. 190. 
