108 
FOSSIL REPTILIA OF THE 
Both Lacertians and Crococlilians differ from Ichthyosaurs in the connections of 
the nasal with the maxillary. The Crocodiles resemble them in the inter-pre- 
maxillary suture ; its presence is an exception in Lacertians, the PJiynchosaurians and 
Rhynchocephalians^ again affording such examples ; I have found it obliterated in a 
Plesiosaurus dolichodeirusr In the position and formation of the palatal nostrils the 
Lacertians agree with, whilst the Crocodiles widely depart from, the Ichthyosaurian 
type. The apertures are distinct or parial in the Plesiosaurs, but are placed far back.^ 
In the structure of the mandible the dentary resembles that element in Lizards, and 
differs from that in Crocodiles, in being pierced externally by a longitudinal series of 
nervovascular foramina ; it differs, also, from the dentary in Crocodiles in its posterior 
termination being above instead of beneath the fore end of the surangular. In the 
amphicoelian Crocodiles the vacuity between the angular and surangular is much 
reduced in size ; it is still smaller in Rhynchocephalians ; it is absent in Ichthyosaurs, as 
in Plesiosaurs^ and most Lizards. 
In the conformation of the posterior angle and the robustness of the articular 
extremity of the mandible the jaw of Ichthyosaurus more nearly resembles that of the 
Crocodiles than of the feebler Lizards, but in the mandibular structures indicative of 
affinity these latter existing Reptiles manifest their closer connection with the Ichthyo- 
saurus. This is conspicuously seen in the absence of distinct alveoli and the lodgment 
of the teeth of both upper and lower jaws in a continuous open channel, the inner wall 
of which, in the mandible, is in a large proportion contributed by the splenial element. 
But the cement-clad base or root of the tooth seems not to become anchylosed to the 
alveolar tract or groove in Ichthyosaurus, but to remain free, till shed, as in Crocodiles. 
Although a portion of the pulp-cavity may persist in the fully developed tooth after the 
base or root becomes consolidated by a mass of interblended osteodentine and cement, into 
this mass the crown of the successional tooth presses, and occasions a cavity by absorption.^ 
In no case have I found evidence of this successive supply of new teeth in the Triassic 
or Permian Theriodonts : herein differs their dentition from both Crocodilian, Dinosaurian, 
Lacertian, and Enaliosaurian Beptilia. 
In most Lizards the hyoid bones present modifications which relate to the size and 
uses of the thick, or long, and commonly bifurcate, tongue. In Ichthyosaurus the appa- 
ratus is reduced to the same number of pieces as in the Crocodile, in which it is less 
1 Monogr. cit., pi. xvi, fig. I, 22 . “On the Affinities of Rhynchosaurus,” ‘Annals and M<ag. of Nat. 
History,’ iv, 1859, p. 237. 
2 Monogr. cit., pi. iii, fig. 1. 
^ Ib., pi. xvi, fig. 2, r, r. 
Monogr. cit., pi. ii. 
® ‘ Catalogue of the Fossil Reptilia and Pisces in the Museum of the College of Surgeons,’ 4to, 1854, 
p. 40, Nos. 139, 140. In No. 141 I point out that in some of the teeth “ the pulp-cavity has been 
obliterated in the crown as well as in the base of the tooth.” See ‘Quarterly Journal of the Geological 
Society’ for May, 1879, pp. 189 and 199. 
