330 CLASS RKPTILIA. 



rate, upper and lower temporal arcades, acrodont teeth, 5-toed 

 limbs, and a parietal organ. The premaxillae are paired, the 

 mandibular symphysis usually ligamentous, the skin has horny 

 scales, and the vertebrae frequently contain persistent remains of 

 the notochord. Anal opening transverse. 



The living genus Sphenodon may be taken as the type of the 

 group. The body is lizard-like in appearance, possessing a 

 scaly skin, a long tail and four pentadactyle limbs adapted for 

 walking. The vertebrae are amphicoelous, the cavities between 

 the centra containing persistent vestiges of the notochord, as 

 in the geckos. Intercentra in the form of subvertebral wedge- 

 bones or chevrons are present on all the vertebrae. The atlas 

 and axis are as in other living reptiles and there is a so-called 

 proatlas as in crocodiles (p. 373). The caudal vertebrae are 

 divided by a septum as in lizards, and the tail when lost is re- 

 produced. The ribs are single-headed, and some of them 

 possess cartilaginous uncinate processes. There is a median 

 sternum to the anterior end of which are attached the coracoids 

 and the interclavicle. Abdominal ribs are present in the form 

 of numerous transverse rows of small splint-bones (three in each 

 row), between the sternum and the pelvis. In the skull (Fig. 

 182) there are paired frontals, parietals and premaxillaries, and 

 a pineal (parietal) foramen. The upper temporal arcade is 

 formed by the postorbital and squamosal, the lower by the jugal 

 and quadrato- jugal which reaches back to the quadrate. The 

 posterior border of the orbit is formed by the postfrontal, post- 

 orbital and jugal. There is an epipterygoid extending from 

 the parietal to the pterygoid and quadrate. The palate is almost 

 entirely bony ; the internal nares are narrow and elongated, 

 immediately external to the vomers, and there is a vacuity 

 between the median parts of the pterygoids. The pterygoids 

 reach back to and are suturally united with the quadrates which 

 are fixed. The bottom of the orbit is almost completely 

 osseous. The dentary pieces of the mandible are united by 

 ligament and not suturally. 



Wien, 102, 1893, p. 250 (and in Ann. Mag. Nat. Hist. (6), 13, p. 297). 

 G. B. Howes and H. Swinnerton, " Development of the skeleton of Sphen- 

 odon," etc., Trans. Zool. Soc, 16, 1901 (contains a bibliography). H. S. 

 Harrison " Development and succession of teeth in Hatteria," Q.J. M.S., 

 44, 1901, p. 161. A. Dendy, Outlines of the Development of the Tuatara, 

 Q.J. M.S. 42, 1899, p. 1. For extinct forms see Woodward, Zittel, op. cit. 



