176 
MR. W. K. PARKER ON THE STRUCTURE AND 
tract under the hind brain ; its greatest width is in front. Another tract, twice as 
large, with its base in front, is seen under the pituitary body, and the triangular super- 
orbitals ( s.ob .) are soft. With these exceptional tracts, all the cranium is solid bone 
up to the middle of the proper nasal region. The fontanelle (fo .) is a long oval; it is 
half the length of the cranial cavity, and half the width of the interorbital region at 
its narrowest part. 
The temporal shoulders of the hind skull are high and large ; from thence the outline 
narrows suddenly, and less rapidly regains its inter-temporal width, so that the inter- 
orbital region is at first very narrow, with a deep, large, crescentic emargination 
right and left; a small round notch is seen between the superorbitals and the ethrno- 
palatines. Then the wide girdle-bone is flat above and concave on each side below ; 
moreover, the edge of the cranial boat is produced outwards, and is scooped below up 
to the optic fenestra. The girdle-bone takes up all the ethmoidal wings, but leaves 
the facial region of the ethmo-palatines untouched ; in front it occupies full half of 
the partition wall, the roof, and the floor of the true nasal region, besides its own 
ethmoidal wall, roof, floor, and wings. 
From below, the skull looks very much like the repetition, in front, of such a 
continuous vertebral tract as is seen in the neck of a Skate. The nerve-passages in this 
flat skull are almost inferior in position, and they form a double series, right and left, 
in a very orderly manner, and are almost equidistant; moreover, those for the 
trigeminal and facial (fig. 7, V.) are subdivided by a bony bar, like those for the glosso¬ 
pharyngeal and vagus (IX., X.) : the optic passage is small. 
The nasal roof (fig. 6, each side of s.n .) is wide behind and narrow in front; the 
floor (fig. 7, s.n.) is wide at both ends and rather contracted, by a crescentic retreat of 
the margin, in the middle. The internal nares (i.n.) are very large, turn inwards in 
front, and lie against the narrowing hind part of the floor. The outer nostrils ( e.n .) 
are only half as large, and half as wide apart; they are well protected by the two 
upper labials (ii.l l .u.l~.) right and left. The snout is not of great extent, but it is 
directly transverse, and has no rostrum; the pro-rhinals (p.rh.) are rather small, but 
the angles of the floor are large and fan-shaped, and lie well within the wide maxil- 
laries (mx.). The ethmo-palatines (e.pa., pa., pg.) are widely transverse, and end in 
an adze-shaped dilatation externally; the palatine bone (pa.) takes on the same 
form, and ends inwardly as a sharp point far from its fellow bone ; the post-palatine 
cartilage is continuous with the pterygoid tract, which is strongly arcuate, but very 
narrow and slight; its bony correlate (pg) runs nearly to the palatine in front, and 
behind, forks at less than a right angle, in which space there is a very large egg- 
shaped Eustachian opening (eu.), the narrow end of which is in the sharp re-entering 
angle of the bone, and is therefore turned outwards. The outer fork binding the 
quadrate bar runs far back; the inner, growing over the stunted “pedicle” (pdf clamps 
it and ties it down to the skull by sutural teeth, instead of allowing it to glide on the 
corresponding cartilage. The quadrate-condyles (g.c.) are twice as large as the occi- 
