DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
159 
The incus ancl stapes have altered very little since the last stage (Plate 22, figs. 10, 
11, i., st.); but the malleus (Plate 22, fig. 12) has lost all its large (metatherian) fore¬ 
growth, only a fine, sharp, processus gracilis ( p.gr .) now remains. 
The hyoid arch (Plate 22, fig. 14) is well ossified, now; the epihyal ( e.hy .) is con¬ 
tinuous with the ear-capsule, above, and is joined to the upper ceratohyal ( c.liy .), 
below, by a tract of non-segmented cartilage. The lower ceratohyal ( c.liy'.) is about 
equal to the upper in size, and the hypohyal ( h.liy .) is only half as long, but broader ; 
all these as well as the basal piece and thyrohyals ( b.h.b.r ., t.hy.) are united by 
joints, mostly with a perfect joint-cavity. The “ annulus” (Plate 21, fig. 1, a.hy.) has 
all its irregular bony nodules confluent with the main bar. 
On the Skull of the Common Mole (Talpa europsea). 
My materials for working out this type have been very copious ; my work links 
itself on to that of Mr. Walter Heape (Quart. Journ. of Micr. Sc., July, 1883), to whom 
I am indebted for some of my best specimens. 
These materials are divisible into arbitrary Stages, as follows :— 
Stage 1.—Embryos of Mole, f of an inch long; (this and the next were measured 
round the curve formed by their head and body, the tail not being reckoned; 
the rest were measured first from snout to occiput, and then from occiput to 
root of tail, and these were added together to give the full length, of course, 
excluding the tail). 
Stage 2.— Embryos of Mole, f of an inch long. 
Stage 3.—Embryos of Mole, 7f and 8 lines (twelfths of an inch) long. 
Stage 4.—Embryos of Mole, § and f of an inch long. 
Stage 5.—Embryos of Mole, 1 inch long. 
Stage 6.—Embryos of Mole, If inch long. 
Stage 7.—Embryos of Mole, If inch long. 
Stage 8. —Ripe young of Mole, If inch long. 
Stage 9.—Young Moles, three or four days old; If and If inch long. 
Stage 10.—Young Moles, 3 inches long. 
Stage 11.—Young Moles, two-thirds grown. 
Stage 12.—Young Moles, three-fourths grown. 
Stage 13.—Adult Moles. 
First Stage.—Embryo of Mole, \ inch long. 
This stage (Plate 16, fig. 1) is, here, merely studied from its outer aspects ; it is 
very profitable for comparison with the corresponding stage in other Mammalia and 
in the Vertebrata, generally; it is nearly half as long as a similar embryo of a large 
Mammal would be. 
About twenty-eight somatomes can be made out; the heart is still seen in a large 
