oi) 
MR. W. K. PARKER OK THE STRUCTURE AND 
cartilage ( o.s .) running from the orbitosphenoicl to the auditory capsules still retains 
its breadth, and is protected by the frontal bone (/.). 
1 7 th Section (Plate 4, fig. 5).—This section is through some very notable parts of 
the skull and its contents. The hemispheres are here at their widest part, and, below, 
the pituitary body (py.) is cut through. Here is the wide splieno-auditory fissure 
(see Plate 2, fig. 6, and Plate 5), over which the large Gasserian ganglion (Y.) lies. 
The frontal ( f ) still protects the posterior band of the orbitosphenoid (o.s.), and 
below this an infero-lateral bone comes into section, namely, the squamosal ( sq .), just 
where it is forming a broad part for the hinge of the lower jaw (cd.p.). Here this bone 
helps to form the cranial wall, in the re-entering angle between the frontal and 
parietal (see Plate 2, fig. 8 ; f ,p.). The dentary bone (cl.) and Meckel’s cartilage 
(ink.) are seen below that mass of superficial cartilage. The dentary (cl.) at its angular 
part here comes close to the pyriform cavity exposed at this part—the tympanic 
cavity (c.ty .); the broad end of this open section is below, and the narrow upper end 
turns a little outwards. 
Below this space the epihyal cartilage (e.hy.) is cut across. Here the faucial 
passage is very narrow below ; above it, the basis cranii is near the basioccipital 
region close behind the postclinoid elevation. The notochord (nc.) lies below, in the 
primary chink between the two parachordal tracts ; and its end is hooked downwards 
(see also Plate 3, fig. 13, nc.), a state of things first shown by Balfour in the Shark 
( ; Elasmobranchs,’ p. 209, Plate 14, figs. 9a and 16 a.) ; and then by me in the Green 
Turtle (‘Challenger’ Reports, Zoology, vol. i., plate 8, figs. 6 and 6 a).* 
The interauditory part of the basis cranii is, here, twice as wide as it is thick; it is 
hollow above, and convex below ; the latter part being split, and having the notochord 
in the fissure. The bulbous end of the cochlear part of the auditory capsule (see fig. 
6, chi.) is here cut across, just exposing the spiral cavity, and showing the apiculated 
fore end. 
18 th Section (Plate 4, fig. G).—The hemispheres (CP), the mid-brain (C 2 .) ; the 
infundibulum, and the pituitary body (py.) are still seen (for the sections are a 
little oblique, and they incline downwards and backwards), but the basis cranii is 
cut through close behind the postpituitary w r all or elevation. The hinder part of 
the Gasserian ganglion (V.) is cut through, and under this the cochlea (chi.) has its 
cavity exposed ; the notochord (nc.) is seen in the chink below, in the solid basi¬ 
occipital cartilage ( b.o.). 
The backward extension of the orbitosphenoid (s.a.c.) is still seen, overlapped here 
by the parietal (p.). The squamosal (sq.) is cut across behind the glenoid cavity, and 
below and within this part, at a moderate distance, Meckel’s cartilage (mlc.) is still 
seen in section. Underand inside it there is a small crescentic tract of bone; this 
* Whatever theory may turn out to he true as to the nature of the prepituitary part of the skull—the 
trabeculae and intertrabecula—we have here a most valuable landmark, for the down-turned end of the 
notochord is certainly the cephalic termination of the axis of the vertebrated creature. 
