180 
MR. W. K. PARKER ON THE STRUCTURE AND 
very large in the Mole, and is half the length of the proper labyrinth, reaching 
backwards almost as far as the inferior turbinals ( Lib .), here largely hidden by the 
inturned nasal wall ( al.sp .). 
The tubular part of the recurrent cartilage is short; the rest is convex below and 
outside, and concave on the other face, where it is in relation to Jacobson’s organ. 
In front of the terminal point of these processes the labyrinth expands rapidly right 
and left, and these moieties are then to be seen a pair of swollen cushion-shaped masses, 
that first bend outwards and then converge towards each other, having only the basal 
beam between them. Where that beam escapes from the vomer it is the perpendicular 
ethmoid (p.e.) ; a little further back it is the presphenoid ( p.s .), and has the stem of 
each ala, or orbitosphenoid (o.s.) ossified ; thence, to the top of the skull, these rapidly 
widening wings are cartilaginous. The posterior sphenoid is a very remarkable 
structure ; it is ossified in its median or basal part only, at present; the anterior 
sphenoid does not develop a median piece, but the basal beam receives its bony 
growth from the ossifying alee. 
The basal region of the posterior sphenoid is at present ossified for about three- 
fifths of its length ; this centre ( b.s .) is very broad, and is alate in front; it is not a 
mere ossified basal beam, for whilst the anterior sphenoid forms its base from its aim, 
the posterior sends its basal bony centre far into the proximal part of its wings— 
right and left. Outside the hinder half of the basisphenoid, where it has narrowed 
in so as to occupy but little more than the proper base (trabecular roots arising from 
parachordals) there, right and left, we see a large rounded boss of cartilage just in 
front of each cochlea (chi.). This swelling part, or process (lg.), at the junction of the 
ala with the base, is homologous with the cartilaginous “ lingula ” seen in the embryos 
of Crocodiles and Birds (Trans. Zool. Soc., vol. ii., part 9, plate 64 ; and Phil. Trans., 
I860, Plate 82). It becomes ossified very variously in these different types, but its 
meaning is the same in all. It is the root of an enlargement for the tympanic cavity— 
the posterior sphenoid becoming pneumatic. Behind these bosses the basal part has 
an elegant “ waist ’’ and then broadens into large “ hips,” on which the cochleee (chi.) 
rest. 
The alisphenoifls (al.s.) are still unossified; they have a very broad proximal part, 
even beyond the cartilaginous bosses and the alee of the basisphenoidal centre; they 
expand so as to grow round the pupiform cochleae, and then are so notched behind as 
to leave a large oval space between their hind margin and the outer part of the 
auditory capsule (chi.). In front of this lateral fontanelle (or fenestra) each alisphenoid 
(al.s.) forms an ear-shaped free lobe, looking inwards and forwards; this lobe is bi- 
perforate for the 2nd and 3rd branches of the 5th nerve (V 3 ., V 3 .). 
There is a cartilaginous tract between the new basisphenoidal and basioccipital 
centres (b.s., b.o.) equal in size to each of these bones; the hinder centre (b.o.) is 
peculiarly reptilian, being at present polygonal, and broader than it is long. The 
chondrocranium is huge in this part of the head ; from the waist-like synchondrosis 
