DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
193 
also is the middle part in front of the synchondrosis, but the sella turcica is badly 
defined. 
The prootic plates ( p.ro '.) have been cut through ; between them and the proper 
bony capsule there is a considerable tract of cartilage. The cochlea (chi.) is much 
masked by bony growths; the meatus interims (VIII.) is large and very near the 
inner edge ; there is a special foramen for the 7th (VII.). 
The remarkable archway over the deep recess for the “ flocculus ” is ossified ; the 
enlargement in front, on the outside, is due to the ampulla of the anterior canal ( a.s.c.), 
and its arch is over the archway; the common sinus for the anterior and posterior 
canals runs, inside the thickening of this curious internal “ porch,” downwards and 
forwards, on the inner side; the appearance of an ampulla below, and in front, where 
it ends, is deceptive, that is due to a swelling of the vestibule (vb.). 
The horizontal canal (/os.c.)is not well seen from this aspect, its ampulla is only 
visible under that of the anterior canal. The posterior canal (p.s.c.) is seen in the 
postero-internal face of the porch where it meets the anterior canal, and where the 
two pass into the common sinus on the inner side. The ampulla of the posterior canal 
is formed after the arch has crossed and passed under that of the horizontal canal, 
just where the latter is entering the vestibule; these parts lie at the bottom of the 
bony labyrinth, just outside the passage for the 9th and 10th nerves (IX., X.). The 
basal, and part of the lateral, regions of the occipital arch ( b.o ., e.o.), are seen, also ; in 
this figure, the hypoglossal nerve (XII.) is on the edge of the exoccipital ossification 
on this inner side ; outside, or below (fig. 5), it is still surrounded by cartilage. 
Inferior arches of the young Mole in the Eleventh Stage. 
The malleus in this eleventh stage is thoroughly Marsupial in character.* 
Seen from the inside (Plate 28, fig. 9) the head projects as a semioval mass, having, 
behind, the saddle-shaped condyloid cartilage. Under the head there is a pneumatic 
recess bordered by a sloping, sinuous edge of bone, from which the manubrium (mb.) 
is continued. That process is rather a round hook than an angular part, and the 
whole hind margin is sinuous, without showing on this face any very definite posterior 
process (ag.p.). The neck of the malleus is broad and irregular; it is followed by a 
rough, rounded, perforated lobe or crest. Then the bone dips and runs forwards as a 
straight “processus gracilis” (p-gr.). But this is only a part of the foregrowths of 
the malleus, for beneath the upper lobe there is a lanceolate, almost distinct tract 
(seen also in fig. 7, tenth stage), and in front of this, running away from the line of 
Meckel’s cartilage (see fig. 7, mk), there is an elegant pretympanic sickle of bone, 
enlarged and split at its end. 
* My own figures of the Marsupial skull will show what I mean by this assertion; meantime the 
reader is referred to Mr. Doran’s valuable paper on the Ossicula auditus (Trans. Linn. Soc., ser. 2, Zool., 
vol. i., plate 64, figs. 15-34). 
MDCCCLXXXV. 2 C 
