The Theromorpha have a longer neck, with at least six and probably seven vertebrae (Fig. 77), as shown by the lengths of the ribs, by the diapophyses, and more definitely by the position of the scapula and clavicles as observed in various specimens. These numbers, six or seven, are those given for the Therapsida, as this order is imperfectly known, and seven is the number that has remained so persistently in their descendants, the mammals. Modern chameleons have but five; true lizards, the Chelonia and Rhynchocephalia, eight; the monitor lizards, Crocodilia, Theropoda, Iguanodontia, and 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.
Fig. 77. Notochordal cervical vertebrae, with intercentra, of Ophiacodon, a primitive theromorph: pa, proatlas; an, arch of atlas; o, odontoid; ax, axis.
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, sixteen 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
