128 
MR W. K. PARKER ON THE STRUCTURE AND 
Plate (22) with the others. Cyclorhamplius is its nearest ally, by far, and in this 
comparison we have dug deeper for evidence of kinship than in any comparison that 
could be made of the skull in the adult. 
Small hind legs have budded out in this larva, and as a correlate of these growths 
three investing and two intrinsic bones have appeared in the skull; these lift it out 
of the sphere of simple “ chondrocrania.” 
The notochord (nc.) is still of considerable size, but the copious development of 
hyaline cartilage has already obliterated several morphological landmarks. 
The occipital condyles ( oc.c.) are now well formed, and the arch itself is very wide, 
rather low, and has a huge doorway ( f.m.). The large oval ear-sacs are completely 
chondrified, and are confluent with the basis and tegmen cranii; they abort its walls 
largely, growing into the sides of the skull; the old lines of junction can, however, be 
traced. 
The cranium proper is very wide, especially behind, and the tegmen is developed, 
already, nearly as much as in Sharks—more than in most Skates ; it has two lesser 
fontanelles in it (fo.). The interorbital part is wide, gently bulging, and gradually 
narrowing to the ethmoidal region, which is now in the act of closing in upon the fore 
part of the brain capsule. Above (fig. 2) the principal fontanelle (fo.) is only a 
quarter the size of the general tegmen of cartilage, and in front it is unenclosed—the 
lateral halves of the primary ethmoidal region of the skull-wall have not met over the 
brain cavity. Also the unfinished state of the skull is seen still further in this, 
namely, that the “perpendicular ethmoid” (p.e.) is still a mere oval upgrowth of 
cartilage—a tuberous ascending development of the intertrabecular tract which is still 
visibly distinct from the trabeculae, all the way from the pituitary floor to where the 
trabeculae become again free in front as the “ cornua” (c.tr.). 
I 21 front of that little swelling of cartilage (fig. 2, p.e.) the foundation of the septum 
nasi is seen in the narrow foremost part of the cartilage which conjugates the two 
trabeculae. 
We get here additional light upon the vegetative growths of cartilage that finish, 
by closing in, the cranial capsule, in front. Where the walls have most converged in 
front they there suddenly grow out as the “ethmoidal wings’’ (al.e.), running by con¬ 
tinuous growth of cartilage into the pterygo-palatine bands (p-pg.). 
The olfactory nerves (l) escape here from inside the thickening wall which gives off 
the wings; in the middle the mesethmoidal “ tuber ” (p.e.) becomes a flatter structure, 
and grows into a vertical partition wall between the nerve-outlets, the foremost of 
the three sense-capsule fenestra. The right and left roofs—growths of the ethmoidal 
wall—unite with each other and with the middle wall; and besides this, in front of 
the cranial cavity, each trabecula at its outside develops a process of cartilage, similar 
to, but less than, the median intertrabecular tuber. These three, growing round the 
olfactory nerves, finish the round passages (fenestrae), and, with the lateral ethmoidal 
walls (growing into the roof), close in the skull-building. 
