274 



Mr. E. S. Goodrich. 



following Huxley (17), believe that the single temporal fossa of the lizard 

 represents the upper fossa of Sphenoclon limited below by the narrow 

 upper temporal bar, while the lower temporal fossa is supposed to have 

 become opened out in the dry Lacertilian skull, the lower bar being repre- 

 sented by a quadrato-jugal ligament. According to this view the Lacertilia 

 are modified Diapsida. Many authors, however, including Baur (2), 

 Williston (35), and Watson (33a), have held that the Lacertilia never had 

 two fossae, and that their skull is, in fact, built on the same plan as that of 

 the Synapsidan Saurotheria (see p. 269). Here, again, an examination of the 

 hind foot and heart (see pp. 264 and 270) shows us at once that the Lacertilia 

 must belong to the Sauropsidan branch. The characteristic mesotarsal 

 articulation and hook-shaped fifth metatarsal are typically developed, the 

 aortic arches are separated and spirally crossed in the Sauropsidan manner. 

 Palaeontology can alone afford convincing proof as to the history of the skull, 

 but the balance of evidence seems to be in favour of Huxley's view. 



List of Some Genera Known to Have Normal Metatarsals. — Mesosauria 

 — Mesosaurus (including Stereosternum). Nothosauria — Lariosaurus (Bou- 

 lenger). Pakeohatteria (Credner). Pelycosauria — Varanosaurus (Williston), 

 Dimetrodon, Ophiacodon (Case), Naosaurus (Osborn), Casea (Williston), 

 Araeoscelis ? (Williston), Pleurosaurus ? (Lortet). 



List of Some Genera Knoivn to Possess a Modified Fifth Metatarsal. — 

 Chelonia — all living and extinct genera. Lacertilia — all living and extinct 

 genera. Ehynchocephalia — Sphenodon, Homceosaurus (Lortet), Saphagosaurus 

 (Gervais), Ehynchosaurus (Huxley), Simcedosaurus (Lemoine), Champso- 

 saurus (Brown). Protorosaurus (H. v. Meyer). Pythonomorpha — Tylo- 

 saurus (Osborn), Mosasaurus (Dollo), Aetosauria — Aetosaurus (v. Huene). 

 Parasuchia — Ehytidodon (McGregor). Crocodilia — all living and extinct 

 genera. Also present, but in a reduced condition, in Dinosauria and 

 Pterosauria. 



Summary. 



The group Eeptilia represents not a true monophyletic class like the 

 class Mammalia and the class Aves, but rather an assemblage or grade of 

 Amniotes retaining a more primitive general structure. The Eeptilia thus 

 include a basal Protosaurian group of amphibian-like forms leading to a 

 central point from which diverge two main branches — the Sauropsidan 

 branch leading to the birds, and the Theropsidan branch leading to the 

 mammals. 



The modern classification of the reptiles, based chiefly on the structure 

 of the skull, is in a very uncertain state. There is a great difference of 



