Total length of very large male specimens up to two feet and a half; in general appearance like many a stoutly built lizard. The general colour of the skin is dark olive-green with small white or yellowish specks on the sides. A series of slightly erectile spines of yellowish colour extends from the top of the head to the end of the tail, but is interrupted on the neck; they are cutaneous, covered with a thin sheath of horn. The under surface is covered with numerous scales, arranged in transverse rows; the rest of the body is rather granular. The tail is thick, slightly compressed laterally. The eye is large, dark brown, with a vertical pupil. Those who are satisfied with superficial resemblances still group this creature with the lizards, but it reveals itself as a primitive reptile or Prosaurian by the following characters, every one of which distinguishes it from the lizards:–The temporal region is bridged by three bony arcades. The large vomers, palatines, and pterygoids form a broad bony roof to the mouth; the large quadrates are firmly fixed by the pterygoids, squamosals, lateral occipital bones, and by the jugal bridge. The vertebrae possess an unbroken series of intercentral wedge-bones. There is an elaborate system of abdominal ribs. The humerus has an entepicondylar foramen, and there is also, in contradistinction to the fossil Rhynchocephalia, an ectepicondylar foramen for the passage of the radial nerve. The carpus still has the primitive number of ten bones, all of which remain separate, including the intermedium. Of soft parts are to be mentioned above all the entire absence of external copulatory organs, _Sphenodon_ being the {295}only recent reptile which is devoid of them; a most primitive condition, sufficient by itself to separate this creature from all the other living reptiles. [Illustration: FIG. 59.–A, Dorsal; B, ventral; C, left-sided view of the skull of _Sphenodon_. × 3/2. _Col_, columella auris; _Cond_, occipital condyle; _E.P_, ectopterygoid; _F_, frontal; _Jug_, jugal; _Max_, maxillary; _Na_, nasal; _No_, anterior nasal opening; _Pal_, palatine; _Par_, parietal; _Pmx_, premaxillary; _Prf_, prefrontal; _Pt.f_, postfrontal and postorbital; _Ptg_, pterygoid or endopterygoid; _Q_, quadrate and quadrato-jugal; _Sq_, squamosal; _Vo_, vomer. See also Fig. 54, B, p. 280.]