PRIME VAL SALAMANDERS. 



which in all the higher Vertebrates are fused together. Nearly all these 

 salamanders are further distinguished by having the chest protected by three 



sculptured bony plates, one of which is central 

 while the other two are lateral ; the position of 

 these plates being shown in our figure of the 

 skeleton, where they are seen on the lower surface 

 of the body, immediately behind the head, under- 

 lying the backbone and ribs. Besides this armour, 

 some species had the whole of the under surface 

 of the body protected by a series of bony scales, 

 arranged in a chevron pattern ; while in a few 

 instances similar scales also invested the upper 

 surface of the body. The majority of the members 

 of the order had the vertebras of the backbone in 

 the form of simple doubly-cupped discs, similar to 

 those of fishes ; but in some of the most primitive 

 types each vertebra consists of four distinct pieces, 

 namely, a single basal piece (i), a pair of lateral 

 pieces (pi), and a single arch and spine (s). Among 

 some reptiles the basal piece remains between 

 two adjacent vertebrae as the intercentrum ; but 

 in the higher forms the other elements coalesce. 

 Since a similar type of vertebra occurs in certain 

 extinct fishes, we have in this structure another 

 bond between the latter and the primeval sala- 

 manders. Brief reference must also be made to the small aperture in the roof 

 of the skull of the primeval salamanders in the bone marked P, since this corre- 

 sponds to one in the skull of the tuatera lizard of New Zealand. In that animal 

 the aperture overlies the rudiment of an 

 eye sunk deep down in the brain and now 

 totally useless, but probably functional in 

 the tuatera's ancestors. The large size of 

 the aperture in the primeval salamanders 

 suggests that the central eye may still have 

 been capable of receiving impressions of 

 light, although we may have to go back to 

 earlier forms before it was of any functional 

 importance as an organ of vision. As in 

 many existing amphibians, teeth frequently 

 occur on the bones of the palate as well as 

 in the margins of the jaws. Another feature 

 of the skulls of many members of the order 

 is the presence of what are called mucous 

 canals in the bones of the upper surface, as shown both in the accompanying figure 

 and in the one on p. 313 ; these canals also occurring in certain fishes. So far as 

 can be ascertained, both external and internal gills generally disappeared in 



SKULL OF THE MASTODONSAUR, WITH THE 

 sci'l.PTUKE OMITTED. 



SO, supraoccipital ; Ep, epiotic ; P, 

 parietal ; Sq, squamosal ; ST, supratem- 

 poral ; QJ, quadratojugal ; Ju, jugal; Pt, 

 postfrontal ; PtO, postorbital; Fr, frontal; 

 PrF, prefrontal ; L, lachrymal ; Na, nasal ; 

 Mx, maxilla. The premaxilla has no letter. 

 (About | nat. size.) 



TWO VERTEBK^E OF A miMEVAL SALAMANDER. 



prz is the anterior and ptz the posterior end. 



