138 MR. W. K. PARKER ON THE STRUCTURE AND 
21st Section (Plate 18, fig. 21).—The anterior canal (a.s.c.) is here cut through where 
it joins the posterior, and the horizontal canal (h.s.c.) is seen where it opens into the 
cavity of the vestibule (lower part of vb.); the wall is imperfect on the inner side 
(see also next stage, Plate 17, fig. 7). The lowest part of the posterior canal, and 
its ampulla, is close behind this part. The posterior lacerated foramen (IX., X.) is 
here cut across, and also the condyloid foramen (XII.) ; the basis cranii (.0.) is large, 
here, and partly ossified. . 
22nd Section (Plate 18, fig. 22).—The thick opisthotic region of the auditory capsule 
is cut across, here, and the posterior canal at its beginning, above, is one with the 
anterior canal (a.s.c.) ; below, it is close to the horizoutal canal (h.s.c.). On the inner 
face the cartilage is thin, and there is a small vestibular cavity (vb.). The supra- 
auditory cartilage (s.a.c.) is so cut across as to be some distance from the top of 
the capsule; this is due to the shght obliquity of the sections. The vagus and 
hypoglossal nerves (XI., X.) are still seen outside the bent basioccipital plate (b.0.). 
This section is in front of the sides and condyles of the occipital arch, and is behind 
the hole for the 12th nerve (XI1.). 
Second Stage of Erinaceus europeus. Young, three-fourths ripe ; 24 inches long ; 
head, * cinch. 
This larger embryo serves well for showing the development of the ectocranium as 
well as for the advancement made in the endocranium (Plate 17, figs. 3-8). Beginning 
with the voof (fig. 4) we find a very orderly series of bony scutes along the mid-line ; 
there are four pairs of these sub-median radiating centres that have all the appearance 
of belonging to the same category, namely, a double row of subcutaneous scales 
growing towards each other along the top of the head. 
The foremost of these scutes, the nasals (n.), ave the smallest, they ave the tiling of 
the cartilaginous nasal roof, and the septum nasi (s.7.) is seen between them. Like 
shell-valves, with a pointed end, forwards, and a rounded broad end, behind, these 
bones just cover the hinder half of the nasal labyrinth. 
The next pair are four times as large, these are the frontals (7); they are narrow 
in the middle and dilated at each end; they scarcely reach the nasals, in front, and 
only touch the parietals (p.), behind, by their convex margin. There is a long 
fontanelle running between them and the parietals up to the nasals, in front, and to 
the supraoccipital (s.o.), behind; this is dilated in three places, especially in the 
coronal region. The concave outer edge of the frontal does not run as far as to the 
supraorbital ridge; this part and the orbital roof are covered with a distinct bone 
(see also fig. 5, s.ob.). This single supraorbital scale bone is new to me in the 
Mammalia, but familiar enough in the Oviparous forms—the Ganoid Fishes, below, 
up to the Tinamous and some higher Carinate Birds, above. In all these, however, 
it is broken up into two or more pieces. 
