134 
MR. W. K. PARKER ON THE STRUCTURE AND 
Below, outside the tongue (tg.) and mouth cavity (m.) the compound lower jaw is 
seen to be composed of three tracts of cartilage and two of bone; the latter answer 
to the dentary and splenial, but these are not actually separate bones, at this 
part. Then there is Meckel’s cartilage, or the primary mandible, and two points of 
cartilage belong to the superficial cartilaginous “ ramus.” 
12 th Section (Plate 18, fig. 12).—Here the razor has cut through the anterior 
sphenoid (p.s.), continuously, missing the small optic foramen (see Plate 17, figs. 1, 2, 
o.s., p.s., II.), most likely cutting in front of it. Thus the cranial cavity and membranous 
cranium is more than half engirdled by this tract; the upper deficiency is, at present, 
only partially made good by the frontal bone. Here we encounter cartilage right and 
left, below the flat presphenoid (o.s.), for the pterygoids are cut through here, and 
they are largely preformed in cartilage (see in next stage, Plate 17, fig. 3 , pg., pg.c.). 
These bones only form a wall, on the right hand, and on the left, to the nasopalatine 
canal ( n.p.c. ), and do not form a bridge, beneath it, as the palatines do. The mandible 
is growing up, here, towards itscoronoid process, above, and its angular process (ag.p.), 
below ; the inner rod ( mk .) lies in a groove of the ramus, near its lower part. 
13 th Section (Plate 18, fig. 13).—This section will be understood if reference is made 
to the dissected skull (Plate 17, figs. 1, 2). The basis cranii is cut through at the hind 
part of the presphenoid (p.s.), just where the basisphenoidal region begins. Here the 
two trabeculae are cemented together by the wedge-like end of the intertrabecula. 
The large sphenoidal fissure is cut through, and several nerve-bundles (V.) are 
seen in the interspace; because of the sinuous form of the margin of the orbito- 
sphenoid (o.s.) that cartilage is cut through twice, immediately in front of the ali- 
sphenoid, which lies in a lower plnne. The bulk of the pterygoid is still cartilaginous, 
and so is the “ ramus” of the mandible (d.) at this part, where the coronoid and 
angular processes (cr.p., cd.p.) are cut across ; Meckel’s cartilage (mk.) forms a 
large oval section at this part, and the dentary is spreading over it; the frontal (f.) is 
seen outside and above the orbitosphenoid (o.s.). 
14 th Section (Plate 18, fig. 14).—This is a very instructive section and should be 
compared with the dissection of the same and of the next stage (Plate 17, figs. 1, 2, 3). 
The cranial cavity with the included brain (CH) is here very large, and the basal part 
of the skull is cut through where the floor is incomplete (b.s., py.), so that we have 
here the exact form of the trabeculae behind the intertrabecula; they are oval, with 
the long axis horizontal. On each side, in a deep fossa, the great Gasserian ganglion 
(V.) is seen, supported by the alisphenoid (al.s.) which lies outside and below the 
general plane of the skull floor and wall; it is ossified at its postero-external margin, 
and its hollow upper face forms the floor of the trigeminal fossa. The orbitosphenoid 
(o.s.) is narrowing towards its posterior band, and it is supported outside by the orbital 
part of the frontal (/.), which runs far down into the hind part of the orbit, almost 
touching the alisphenoid. 
Two rods of cartilage, oval in section, but with their long axis vertical, are seen 
