176 MR. W. K. PARKER ON THE STRUCTURE AND 
under the proximal part of this rod, where the malleal enlargement is, there is a small 
ectosteal tract ; the future bony centre of the malleus. Also in the thick soft outer 
disk of the tympanum there is a crescentic deposit of bone—the annulus. In this, 
as in the rest, the short crus of the incus (7) is small and bent downwards; its 
symplectic facet, the orbicular region of the long crus, is shown with the outline of 
the base of the stapes (st.) round it ; this is the inner view of these parts. The epihyal 
(e.hy.) is drawn as cut away from the auditory capsule; its lower end is connected 
with the pointed top of the ceratohyal (c.hy.), the long upper piece of which is 
beginning to ossify ; the lower piece (¢.hy’.) is no longer than the hypohyal (h.hy.), 
oO 
which is thick and curved. The basi-thyrohyal piece (b/.b7., thy.) is thick and 
roughly U-shaped, with its angles squarish. 
Seventh Stage.—A sinilar dissection to the last of an older embryo Mole ; 14 inch long. 
This fifth inner view of the visceral arches (Plate 28, fig. 5.) shows another sign of 
advanced growth ; the distal ossification of Mrckern’s cartilage is almost surrounded 
by a splenial growth of the dentary (d.), forming the inner face of the mandible. The 
dentary is also growing well round the thick tract that ends, above and behind, in the 
condyloid process (cd.p.); this is capped by the glenoidal tract (gl.c.), a part derived 
from the same superficial source. The soft disk round the membrana tympani (77.ty.) is 
a more developed crescent of bone—the annulus (a.ty.). The head, both of the malleus 
and. incus (ml.,7.), is smooth and rounded, and in each case has a very condyloid appear- 
ance; the stapes (s¢.) is detached from the orbicular facet of the incus (¢.); it is a 
stout cartilage, with a small circular hole, a distinct neck below its incudal head and 
facet, and a thick rim to its base, or proximal plate. I see no interhyal (_ intra- 
stapedial) nucleus of cartilage in the tendon of the stapedius muscle (st.m.). 
Eighth Stage—Vertical longitudinal section of the head of a ripe embryo Mole ; 
13 inch long from snout to root of tail. 
In this preparation the interior of the right half of the skull was displayed with the 
whole of the ethmoseptal part of the cranial axis. 
The figure (Plate 25, fig. 1) will help to a proper understanding of the skull in its 
earlier stages, both the sections and the dissections (Plates 23-25). The endocranium 
is now undergoing ossification. The nasal region, from the back of the cribriform 
plate to the front of the snout, is exactly of the same length as the cranium, measured 
from the former point to the top of the foramen magnum. The great internasal septum 
(s.2., p.e.) is twice as high behind, at the crista galli (ev.g.), than in front, between the 
nostrils ; the dorsal line of this wall is sinuous; its lower edge is gently concave ; 
behind the presphenoidal region (/.s.), the lower line of the skull is gently convex, 
Between the nostrils, the floor and wall together form a sinuous tract ; behind this 
part the calinasal artilage gives off the recurrent (or JACoBsoN’s) cartilage, right and 
left (ve.c.). The great intertrabecular bar thickens the septum all along, giving its 
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