DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 209 
epihyal (e.hy.) has fused with the auditory capsule; here the bone (aw.) extends; but 
the main part of the unusually well-developed epihyal is still cartilaginous, and is 
continued without any segmentation into the unossified part of the ceratohyal 
(Plate 29, fig. 6; and Plate 31, fig. 12, c.hy.). Half the upper ceratohyal is ossified— 
its middle part; then comes a joint, and then the short, lower ceratohyal (c.hy’.), 
which, in turn, articulates with the short, ossifying hypohyal (h.hy.). 
The latter, in turn, articulates with the almost straight, transverse, nearly ossified 
basihyal (b.4.b7.), which has, articulating with it, the ossified, short thyrohyal rods 
(t.hy.). 
Third Stage (concluded) —Vertically transverse sections of the Nestling Shrew. 
A description of these sections will throw further light upon the structure of the 
skull at this stage. 
Section 1 (Plate 30, fig. 1)—This is through the outer nostrils (e.7.), and shows 
how the roof (a/.n.) turns inwards to form the narial valve, and how the floor, also, of 
the opening, is cartilaginous ; many of the vibrisse are seen in section in the thick 
skin of the snout, in this, and in the following sections. 
Section 2.—Here (Plate 30, fig. 2) the narial valve is seen in the hind part of each 
nostril; it curves downwards at its free end; the ale nasi (al.n.) are confluent, back 
to back. 
Section 3.--In this (Plate 30, fig. 3) there is a definite tract of the septum nasi 
(s.n.) with an enlarged—intertrabecular 
base. The narial valve is gone, and the 
cartilage that formed it is now confluent with the floor, so that there are two perfect 
narial tubes (7.p.) at this part. 
Section 4.—At this part (Plate 30, fig. 4) the floor and walls are separating, again ; 
the floor, right and left, touches the lower part of the septum, which is carinate below 
its bulbous part. 
Section 5.—The tubes now (Plate 30, fig. 5) are not surrounded, below, by cartilage, 
and the floor is in two short, oblique tracts; the almost vertical wall turns inwards 
below, and the septum, still carinate, is much thicker; these narrow floor-tracts are 
those that give off JAcoBson’s (=recurrent) cartilages (Plate 29, fig. 5). 
Section 6.—We are now (Plate 30, fig. 6) behind the snout, and through the 
premaxillary (px.), with its thin walls, and its relatively huge incisor teeth (see also 
fig. 7, t.) just developing in these large, swelling pulps. The double tube is con- 
tracted here, the top is still flat, and the septum (s.7.) is very thin above and thick 
below ; the enlargement at the bottom of each inturned wall (al.sp.) is the rudi- 
ment of the inferior turbinal (7.tb.), at its very beginning, in front. The rods of 
the recurrent cartilages (7c.c.) are seen lying obliquely below the bulbous intertra- 
becula (s.7.); below, the fore part of the lower lips are seen in front of the dentary 
bones (i7.). 
Section 7.—This (Plate 30, figs. 7, 7A) 1s through the fore part of JAcoBson’s 
MDCCCLXXXV. 2 
