198 PROF. W. K. PARKER ON THE STRUCTURE AND 
B. The Endocranium of the same Larva of Triton cristatus. 
This structure is very instructive, and is already very complete both in its general 
finish and in the development of the osseous centres. 
The occipital condyles (oc. ¢) are large, oval, pedunculate, posterior, and somewhat 
inturned. The foramen magnum is directly posterior, and both above and below the 
skull has a large round notch between the projecting condyles; this is filled below by 
the large oblong “ odontoid rudiment ” (od. v). 
That process is seen to be due to the development of a small intercalary vertebra 
(figs. 8, 4, od. v), the symmetrical parts of which are two small nodules of cartilage close 
to the edge of the basioccipital investing mass (v7”). 
The large space which the notochord runs through between the basis cranii and the 
first perfect vertebra (v7’) is seen to be thus utilized; a new separate bony sheath is 
formed on the notochord at that part, in front of that which encloses the pith of the 
vertebra; and behind the cranial part this has already, in this larva, coalesced with the 
former. 
This bony rod has the unossified lateral rudiments (fig. 4, 7v') attached to its narrow 
fore part; they will be ossified from it afterwards; and thus the “ odontoid” rudiment 
will become much broader. 
The cartilage of the skull-floor has grown in front of the large cephalostyle (c.st) ; 
and a new tract of cartilage, now already confluent with the hinder or parachordal 
part of the trabecule, fills up the space as far as to the edge of the foramen 
magnum. 
Through this unossified tract (7, iv) the notochord (c.st) runs; the foremost larger 
half of it is invested with the foremost bony sheath, the apex of which in the retracted 
condition of the notochord lies behind the flat “ postclinoid ” region, in which there is 
no “posterior basicranial fontanelle.” Thus a vertebral rudiment breaks out in the 
fore part of the basioccipital region, a region which is related to the seventh (and 
eighth), ninth, and tenth nerves in these Ichthyopsida, and therefore not comparable 
to one vertebral (spinal) segment, but to a regional series of such segments. 
The basicranial floor (fig. 3) is occupied by the large fontanelle from the post- 
clinoidal to the ethmoidal regions; it is shaped like a long egg, with the broad end 
foremost ; its enclosure is formed entirely by the trabecule. 
The auditory capsules (aw) are more oval and more oblique; they are turned outwards 
in front, and are now marked more evidently by the arched canals and bulbs of the 
membranous labyrinth within. 
They have to be studied with the hinder skull; for they are floored by the para- 
chordal cartilage, which runs outwards on each side as far as to the fenestra ovalis 
and stapes (st), and, creeping round under the fore part of the capsules, appear in 
front on the upper face of each capsule close behind the ascending processes of the 
suspensoria (fig. 2, a. p). 
