198 MR. W. K. PARKER ON THE STRUCTURE AND 
Along the annular folds of the outer skin the bud-like hair-pulps are seen cropping 
up in corresponding rows, as though they had been planted by a farmer’s “ drill.” 
The eyelids are developed, and closed over the eye-balls ; the concha auris is a kidney- 
shaped fold of skin, the snout is, relatively, no longer than that of a full-grown 
Mastiff, and shows little promise, as yet, of its future length. 
Second Stage.—Ripe embryos of Sorex vulgaris, 9$ lines long 
(about 4 of an inch, or 20 im.). 
The chondrocranium (Plate 29, fig. 7), is undergoing ossification, but its general form 
is not altered, and absorption of those parts of the cartilage which do not ossify has 
scarcely set in; it serves well at this stage for comparison with the skulls of the Mole 
and the Hedgehog at a similar stage of development (see Plates 17 and 25). In the 
Mole the chondrocranium is less massive, relatively, than in the Hedgehog, and in the 
Shrew less than in the Mole. The Hedgehog is the least modified and most. pri- 
mitive type. The Shrew is the most modified, and that mainly through dwarfing, so 
that some parts ave arrested, and others actually suppressed—as if for want of room 
for them. They may easily have arisen from one common stock, and the Mole comes 
in as a connecting link between the well-developed Hedgehog and the scant and 
stinted form of the Shrew.* 
Therefore we may look for signs of that peculiar form of degeneration which arises 
from dwarfing. The cartilage may be expected to be scanty, and the number of 
osseous centres lessened. : 
In this ripe embryo of the Shrew the top of the nasal partition wall (Plate 29, 
fig. 7, 8.1., p.e.) reaches half-way back to the front of the supraoccipital (s.0.); at its crown 
it is much more than half the height of the skull; at its base, from the front of the 
snout (al.n,) to the middle of the presphenoid ().s.), it is twice as long as from that 
point to the foramen magnum. 
The snout, itself, has only half the relative length it will have in ten or twelve 
days——next stage (Plate 29, figs. 1-4). The septum in front is perforated and 
circular ; then it narrows to half its width in front, and is narrowest in the front part 
of the true septal region, behind the snout, proper. Thus between the large recurrent 
or JACOBSON’S cartilages (¢c.c.)+ the thick intertrabecular base of the whole partition 
wall (7.t7.) is formed into a low arch, and is especially thick where it descends again, as 
it passes backwards towards the presphenoidal region. The thinner, main part of the 
partition—septum nasi (s.7.), and perpendicular ethmoid (p.e.)—is very even, and forms 
a low triangle, the hinder side of which is the shortest, and is the dividing line 
between the two perforated (cribriform) plates (c7.p.) ; that line is a little arched, the 
longer line in front, towards the snout (a/.sp.) is first convex, and then concave before 
* The pygmy Shrew (Sorex pygmcus), is not only the smallest British Mammal; it is as nearly as may 
be the smallest beast in the whole Class of the Mammalia. 
+ For te.c. read rec. 
