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Mr. E. S. Goodrich. 



present we may be content with keeping the class Eeptilia, always 

 remembering that it is a grade of ill-defined limits. 



The modern views of the phylogenetic relationships of the various orders 

 of Eeptilia may be said to have arisen chiefly from the work of Cope and 

 Baur, following on the conclusions of Huxley and other earlier authors. To 

 the ingenuity of Cope we owe the valuable suggestion that the starting- 

 point of the divergence between the Amphibia and the Eeptilia was 

 determined by the structure of the vertebral column — the vertebral body 

 being mainly derived from the hypocentrum in the former and from the 

 pleurocentrum in the Amniota. Being thus provided with a means of 

 distinguishing the early reptiles from their -Amphibian relatives, the next 

 step is to seek for characters enabling us to trace out the diverging lines 

 among the Eeptilia themselves. Here again we are indebted to Cope (13), 

 but more especially to Baur (1, 2) for pointing out the importance of the 

 roofing of the skull in classification. Whereas the earliest and most 

 primitive reptiles have, like their Amphibian ancestors, a roofing complete 

 over the temporal region, this becomes pierced in others- by one or two 

 foramina. Thus are left one or two longitudinal temporal arches. The 

 formation of the foramina or fossse is generally accompanied by a reduction 

 in the number of bones covering the hinder region of the skull. It is not 

 my intention to enter into a detailed account of these points in this paper ; 

 they have been discussed by many authors, and are well understood. It 

 will be sufficient for our present purpose to point out how profoundly 

 the modern classification of the Amniota has been affected by their 

 recognition. 



Owen and Cope long ago drew attention to the Mammalian affinities 

 of certain fossil reptiles now included in the orders Cotylosauria and 

 Theromorpha ; while Huxley emphasised the relationship of the birds to the 

 other orders, more especially the Crocodilia and. the Dinosauria. Huxley, 

 indeed, included the Eeptilia with the Aves in the group Sauropsida, and 

 believed the Mammalia to have been independently derived from more 

 Amphibian-1 ancestors. He failed at that time (17) to appreciate the fact 

 that his gr„.^r oauropsida included forms, like the Dicynodontia and the 

 Sauropterygia, which belong in all probability to the Mammalian line. 



When, chiefly owing to the remarkable discoveries of Seeley and Broom, 

 the true affinities of the extinct Theromorpha became established, the 

 tendency to split the Eeptilia into two diverging branches became more 

 pronounced. The importance of the skull-roofing in this connection was 

 appreciated by A. Smith Woodward (37), but it was not till 1903 that 

 Osborn definitely attempted to divide the whole class Eeptilia into two 



