300 PROF. W. K. PARKER ON THE STRUCTURE AND 
and these wings are direct upgrowths of the paired trabecule, which grow, like new 
shoots, from the under surface of the upturned parachordals. 
In front of the pituitary involution, there being no axial notochord, a new aais 
appears; this preavial rod, the “intertrabecula,” is very large indeed in the second 
stage in this type. It is seldom absent (as in the Ophidia), but in all forms that have 
a projecting snout this bar, rod, or plate forms the axis of such foregrowth of the skull, 
and may be equally hypertrophied in the Mammals (Cetacea) as in the Elasmobranchs 
(Pristide). 
The Crocodilia, as this stage shows, have inherited a compound nasal labyrinth—(a) the 
valvular cartilage outside (in front), (4) the ethmoidal region, behind, (¢) the proper 
nasal roofs, and (d) the middle wall formed by the intertrabecula; these are all chon- 
drified continuously, and we must go down to the Amphibians, Elasmobranchs, and 
Marsipobranchs for a true interpretation of what is seen in these high Reptiles. 
In this stage the clefts are fast closing in, and the inner opening of the persistent 
pouch, the first or tympanic cleft, is a mere crescentic slit, and corresponds to what is 
permanent in some Batrachia. 
Instead of the ichthyic, large, symmetrical, perforated pharynx there is here a mere 
funnel-shaped enlargement of the fore end of the cesophagus; and only three of the 
visceral arches are developed at all, whilst only the first attains to its full size. 
With the total loss of branchial function there is an extraordinary amount of new 
specialization; and only by tracing out the early stages can a true interpretation of the 
parts be made. 
In this stage the first and second visceral arches, if compared with those of the 
Elasmobranchs, Chimeeroids, and Urodeles, will be found to be normal, or nearly so. 
There are only two main segments on each side in the mandibular arch, viz. the 
pterygo-quadrate and the articulo-Meckelian. The pier of this foremost arch has a huge 
‘otic process,” and a rudimentary “pedicle ” with two forks—one a small “ ascending 
process,” and the other a small “ pterygoid cartilage.” 
The next arch has several normal branchial segments, like its counterpart, the hyoid 
of Chimera; but it has also supernumerary segments like those seen in Acipenser and 
in other Ganoids. As in many Selachians, its pharyngo-hyal or upper joint pushes 
itself into the side of the auditory capsule; below this there is an epihyal and a 
ceratohyal, the latter stopping short behind the hinge of the mandible, and becoming 
solid continuously with the articular head of that part, its proper serial homologue. 
Distally there is but a small region of basihyal cartilage continuous with that of the 
third arch or first branchial, proper. That arch has merely a small pair of cerato- 
branchials. 
Passing on to the third and fourth stages, we find that the whole of the chondro- 
cranium (with its visceral arches) has become Sawropsidan, and the investing bones, 
which are now demonstrable, are in number and relation quite Crocodilian. 
