268o 



earlier fishes; and a resemblance to that group is also shown by the paired supraoc- 

 cipital bones (SO), 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 cen- 

 tral while the other two are lateral; the position of 

 these plates being shown in our figure of the skel- 

 eton, where they are seen on the lower surface of 

 the body, immediately behind the head, underly- 

 ing the backbone and ribs. Besides this armor, 

 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 in- 

 stances similar scales also invested the upper sur- 

 face of the body. The majority of the members 

 of the order had the vertebrae 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 

 SKULL OF THE MASTODONSAUR, WITH pieces, namely, a single basal piece (z), a pair of 

 THE SCULPTURE OMITTED. lateral pieces (pi), and a single arch and spine 



(s). Among some reptiles the basal piece re- 



(About one-eighth natural size. ) 



SO. supraoccipital; Ep. epiotic; P. parietal; . , ,. , 



s q . squamosai; ST. supratemporai; QJ. quad- mams between two adjacent vertebrae as the mter- 



ratojugal; Ju. jugal; Pt. postfrontal; PtO. rpr ,t rnTn . K t1 t i n flip \\\o\\e-r forms the Other 

 postorbital; Fr. frontal; PrF. prefrontal; L. Centrum, I 



lachrymal; Na. nasal; MX. maxiiia. The elements coalesce. Since a similar type of verte- 



premaxilla has no letter. 



bra occurs in certain extinct fishes, we have in this 



structure another bond between the latter and the primeval salamanders. 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 corresponds 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 to- 

 tally useless, but probably functional in the 

 tuatera's ancestors. The large size of the 

 aperture in the primeval salamanders sug- 

 gests 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 func- 

 tional 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. An- 

 other 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 above 



TWO VERTEBRA OF A PRIMEVAL 



SALAMANDER. 

 prz is the anterior and ptz the posterior end. 



