184 
MR. W. K. PARKER ON THE STRUCTURE AND 
inner side (Plate 28, fig. 6). Here Ave see that the deep and the superficial mandibles 
are both well developed; the basal cartilage (basimandibular, b.mn.) is still large at 
the symphysis, and the subdistal part of Meckel’s rod (ink), although undergoing 
ossification ( mk'.), and hidden partly by the splenial lamina of the dentary (cl.), is still 
perfect up to its malleal end (ml.). That part (ml., mb.) is now undergoing endostis, 
answering to the ectosteal plate applied to it; but the incus (i.) and the stapes (st.) 
are still unossified. The annulus ( a.ty .) is growing larger round the membrana 
tympani (m.ty.), but the fold of skin that lies outside that membrane is still A T ery 
thick and spongy. The cartilage that pre-forms so much of the permanent mandible 
is very solid, now; on the articular or condyloid process the glenoidal facet ( gl.c .) is 
figured, like a cap; it was derived from the same primary subcutaneous tract, and has 
the same morphological meaning, as the slab Avhich is ossified by the dentary bone. 
Tenth Stage. — Young Moles; 3 inches long from snout to root of tail. 
When the young are more than one-third longer than in the last instance we get a 
great advance towards the permanent condition. 
In the side view of the skull (Plate 27, fig. 3) the jugal, squamosal, lower jaw, and 
most of the hyoid arch are left out. 
The long, non-segmented, decurved snout (al.n.) reaches half-way to the badly- 
formed orbit. The valvular nostril (e.n.) is almost terminal, and is seen best in the 
under face. The facial part of the premaxillary (px.) is half as large as that of the 
maxillary (mx.); at present the canal for the maxillary nerve (V 3 .) is not finished 
externally. On the process above it the small crescentic lachrymal (l.) rests, and the 
canal (l.c.) is seen in front of the bone, on the face. The slender nasals (n.) and the 
small frontals (f ) are still distinct from each other, and from the facial plates of the 
bones below them (px., mx.). The large parietal (p.) always keeps distinct from its 
surroundings: the interparietal (i.p.) is now a broad, transverse plate between the 
parietal and the supraoccipital (s.o.). The palatine (pa.) and the pterygoid ( pg.), 
Avith its terminal cartilage (pg.c.) still visible, can be seen below and behind them, the 
annulus (a.ty.). Behind the lachrymal (l.) the thin convex frontal shell (f.) is turned 
inwards suddenly in its orbital part. Near the hind corner of the orbital plate the 
opening for the ophthalmic nerve (V 1 .) is large and oval. BeloAv that bony plate the 
lateral ethmoidal mass (al.e.), and the cartilaginous top and bony lower part of the 
orbitosplienoid ( o.s .) can be seen, as also the emerging optic nerve (II.). The ali - 
sphenoid, Avith its two large foramina (V 2 ., V 3 .), is seen outside and behind the orbito- 
sphenoid ; below their foramina the broad basisphenoid ( t.b.s.) is exposed. Over 
the drum of the ear (a.ty.) Ave see the large four-sided, infero-lateral fontanelle 
(fo.), which is hidden in the perfect skull by the squamosal. Behind that mem¬ 
branous space a deep tempered bone is shown ; it is large, convex, and has a polygonal 
outline; this is the prootic (pr.o'.), which has rambled away from the labyrinth, to 
