lOO 



THE OSTEOLOGY OF THE REPTH^ES 



The Theromorpha have a longer neck, with at least six and prob- 

 ably seven vertebrae (Fig. 77), as shown by the lengths of the ribs, 

 by the diapophyses, and mored efinitely by the position of the scap- 

 ula and clavicles as observed in various specimens. These numbers, 

 six or seven, are those given for the Therapsida, as this order is im- 

 perfectly known, and seven is the number that has remained so per- 

 sistently in their descendants, the mammals. Modern chameleons 

 have but five; true lizards, the Chelonia and Rhynchocephalia, eight; 

 the monitor lizards, Crocodilia, Theropoda, Iguanodontia, and 



Fig. 77. Notochordal cervical vertebrae, with intercentra, of Ophiacodon, a 

 primitive theromorph: pa, proatlas; an, arch of atlas; o, odontoid; ax, axis. 



Ceratopsia, nine; the Pterosauria and Phytosauria, eight or nine; 

 the Pseudosuchia, eight to ten; the Trachodontia and Sauropoda, as 

 many as fifteen. It must be remembered, however, that in some 

 cases these numbers are only approximately correct, dependent 

 upon the interpretation of what constitutes a cervical vertebra by 

 different observers. 



On the other hand, among strictly amphibious or aquatic reptiles 

 there has been an increase or decrease in the number, the latter in 

 the tail-propelling aquatic types. The ancient proganosaurs have 

 ten or eleven; the dolichosaur lizards, thirteen; the nothosaurs, six- 

 teen to twenty-one or twenty- two; the plesiosaurs, from thirteen to 

 as many as seventy-six; probably also the increase in number among 

 the trachodont and sauropod dinosaurs may be attributed to water 



