3 12 
PRIMEVAL 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 vertebrae of the backbone in 
the form of simple doubly-cuj)ped 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 
SCULPTURE 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; iVa, nasal ; 
Mx, maxilla. The premaxilla has no letter. 
(About | nat. size.) 
TWO VERTEBRAE OF A PRIMEVAL SALAMANDER. 
prz is the anterior and ptz the posterior end. 
