ON FOSSIL AND RECENT REPTILIA. 161 



region between the exoccipitals and tympanies, the parietal foramen, the 

 zygomatic extension of the post-frontal, the palato- maxillary and pterygo- 

 sphenoid vacuities in the bony palate ; and all these are Lacertian characters 

 as contradistinguished from Crocodilian ones. But the antorbital vacuities 

 between the nasal, pre-frontal, and maxillary bones, are the sole external nos- 

 trils in the Plesiosaurs : the zygomatic arch abuts against the fore part of the 

 tympanic, and fixes it : a much greater extent of the roof of the mouth is 

 ossified than in lizards, and the palato-maxillary and pterygosphenoid fissures 

 are reduced to small size : the teeth, finally, are implanted in distinct sockets. 

 That the Plesiosaur had the ' head of a lizard' is an emphatic mode of express- 

 ing the amount of resemblance in their cranial conformation : the crocodilian 

 affinities, however, are not confined to the teeth, but are exemplified in some 

 particulars of the structure of the skull itself. 



In the simple mode of articulation of the ribs, the Lacertian affinity is 

 again strongly manifested ; but to this vertebral character such affinity is 

 limited : all the others exemplify the ordinal distinction of the Plesiosaurs 

 from known existing Reptiles. The shape of the joints of the centrums; the 

 number of vertebrae between the head and tail, especially of those of the 

 neck ; the slight indication of the sacral vertebra? ; the non-confluence of the 

 caudal haemapophyses with each other; are all ' plesiosauroid.' In the size 

 and number of the abdominal ribs and sternum, may, perhaps, be discerned a 

 first step in that series of development of the haemapophyses of the trunk, 

 which reaches its maximum in the plastron of the Chelonia. 



The connation of the clavicle with the scapula is common to the Chelonia 

 with the Plesiosauri ; the expansion of the coracoid — extreme in Plesiosauri, 

 — is greater in Chelonia than in Crocodilia, but is still greater in some 

 Lacertia. The form and proportions of the pubis and ischium, as compared 

 with the ilium, in the pelvic arch of the Plesiosauri, find their nearest 

 approach in the pelvis of marine Chelonia ; and no other existing Reptile 

 now offers so near, although it be so remote, a resemblance to the structure 

 of the paddles of the Plesiosauri. 



Both Nothosaurus and Pistosaurus had many neck-vertebrae ; and the 

 transition from these to the dorsal series was effected, as in Plesiosaurus, by 

 the ascent of the rib-surface from the centrum to the neurapophysis ; but 

 the surface, when divided between the two elements, projected further out- 

 wards than in most Plesiosauri. 



In both Notho- and Pistosaurus, the pelvic vertebra developes a combined 

 process (par- and di-apophysis), but of relatively larger, vertically longer, 

 size, standing well out, and from near the fore part of the side of the verte- 

 bra. This process, with the coalesced riblet, indicates a stronger ilium, and 

 a firmer base of attachment of the hind limb to the trunk than in Plesio- 

 saurus. Both this structure and the greater length of the bones of the fore- 

 arm and leg show that the Muschelkalk predecessors of the Liassic Plesio- 

 sauri were better organized than they for occasional progression on dry land. 



Order V. Anomodontia*. 



This order is represented by three families, all the species of which are 

 extinct, and appear to have been restricted to the Triassic period. In it the 

 teeth are wanting, or are confluent with tusk-shaped premaxillaries, or are 

 confined to a single pair in the upper jaw having the form and proportions of 

 canine tusks. The skull shows a 'foramen parietale' and two nostrils: the 

 tympanic pedicle is fixed. The vertebrae are biconcave : the pleurapophyses 



* avofios, lawless; 6$ovs, tooth. 

 1859. m 



