550 
ME. W. K. PAEKEE ON THE STEUCTUEE AND DEVELOPMENT 
a large number of types) the rule is for the pterygoid bones to grow forwards to the hind 
part of the vomer (or vomers), and afterwards, as in Anguis fragilis , for the pointed 
anterior part of each to become segmented off as a mesopterygoid. This segment loosed 
from the pterygoid then coalesces with the upper edge of the inner part of the main 
palatine bone (“ Skull of iEgithognathous Birds,” Trans. Zool. Soc. 1875, plates 54-62)*. 
Fifth Stage. Young Axolotls 1-j inch long. 
In this stage (Plate 22. figs. 6, 7) the chondrocranium shows several points in advance 
of what was seen in the last. The two pairs of basilar cartilages have united with each 
other and with the auditory capsules, and, leaving out the postmandibular arches, all 
but the new parts are welded together ; so that we have now a cartilaginous skull 
exactly comparable to that of the Elasmobranch (excepting, of course, the lack of the 
tessellated calcifications). 
The occipital condyles (fig. 7, oc.c.) are now fashioned, and in front of them the basilar 
cartilage has sent a lip right and left beneath the notochord ( nc .). These basilar lips 
are distinct, and so also are the crests that have grown upwards from the basilar plate to 
form the ex- and s^pra-occipital regions of cartilage (figs. 6, 7, e.o., s.o.). 
The notochord is not only belted below, it is also capped with the increased and 
increasing bony cephalostyle ; a broad selvedge of cartilage also passes between this 
rudimentary cranial “ centrum ” and the pituitary body ; it is a flat postclinoid conju- 
gation of the trabecular parachordal tracts. 
The prechordal part of the trabeculae now exists as a high wall from the auditory to 
the nasal sacs ; and this wall, convex without and concave within, is turned over a little 
into the roof, and to a greater degree into the floor. But the roof is open from end to 
end, and the floor is a gaping space for the foremost three fifths of its extent. 
But the vicarious exoskeleton keeps up with the requirements of this openwork of 
cartilage. 
The conjugational “ internasal plate” ( i.n.c .) is thickening, especially at the middle, 
and its hinder margin has become convex ; it has retained its relative extent antero- 
posteriorly ; but the lateral leafy growths, the cornua trabeculae ( c.tr .), are now large 
flabelliform outgrowths, having an emargination between them which forms three fourths 
of a circle. The anterior conjugation of the trabeculae (internasal plate) may well be 
the foremost growth of the curiously generalized basilar and neural parts of the skeletal 
axis ; yet, dying out here in the frontal wall, they have sent out a pair of pleural 
rudiments. 
But behind the internasal band there is a pair of 44 pleural rudiments ” which are not 
mere outgrowths. They are separate elements ; these are the antorbital cartilages or 
ethmopalatines ( e.pa .). 
* We shall soon come to a modification, by segmentation and displacement, of this primary pterygo-palatine 
hone that will tax our knowledge of these parts and the interpretation of them in a large series of Vertebrate 
types. 
