DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 133 
mass—the precurrent cartilage (pc.c.) at its hind part; in the next section (fig. 9) 
it forms the front projecting part, inwards, of the middle turbinal (m.tb.). 
The vomer (v.) is here cut through its middle, where it is roughly carinate ; 
afterwards, this part will rest on the palatine plates of the maxillaries. These bones 
(mx.) have here developed a large alveolar cavity, and a tooth-pulp is seen in the 
alveolus ; the nasals have their place taken by the frontals (f). In the last, and in 
this, the mucous crypts (m.g.) are abundant, especially below. The large oval section 
of MEcKEL’s cartilage (mk.) is now overgrown with the diploé of the dentary (d.), 
which also is developing an alveolus, with its tooth. 
9th Section (Plate 18, fig. 9).—Here another partial section is given through the 
forepart of the eye-ball (e.), and the middle of the rhinencephalon which is giving off 
its fibres through a mainly membranous cribiform plate (er.p.). Here the septum (p.e.) 
is much lower, and beneath it the vomer (v.) is beginning to divide into its hind forks. 
The folds of cartilage are, here, confluent, so that the nasal passage is now in several 
sections, and at the lower part a section of the space is growing towards the cavity 
of the other side ready to form the proper “nasopalatine canal.” The maxillaries 
and dentaries (m., d.) have here large alveoli with their tooth-pulps; the superficial 
bone, above, is the widening frontal. 
10th Section (Plate 18, fig. 10).—This is another partial section, made through the 
middle of the eye-ball (e.), and the hind part of the nasal labyrinth, with the huge 
olfactory lobes (rhinencephala) overlying a membranous cribriform plate. The nasal 
wall now forms a protection to the “ fossa,” and beneath the floor (nf) the cartilage 
runs nearly up to the low dividing wall (p.e.). Here the labyrinth is reduced to 
two passages (i.p.), besides the common nasopalatine canal (7.p.c.) at the mid- 
line, below. Here the forks of the vomer (v.) are cut across, and at this part the 
maxillary meets the palatine ( pa.) on the palatal floor; outside, the former bone (mz.) 
shows its large alveolar plates, as does the dentary (d.), below. At this part the 
frontal is in reality in two pieces, as the next stage will show; the orbital plate being 
separate from the upper part (/.). 
L1th Section (Plate 18, fig. 11).—This section is through the back part of the eye- 
ball (e.) and the front third of the hemispheres (C!’.). Here the true cranium comes 
into the section, for the basal beam is now the presphenoid (p.s.), and the wall right 
and left is the orbitosphenoid (0.s.). 
The back of the olfactory labyrinth (n.w.) is cut through, and these limited tracts of 
cartilage lie between the two regions of the anterior sphenoid (0.s., p.s.), and are con- 
fluent with the basal mass. So, also, is the orbitosphenoid confluent, above, with the 
top of the olfactory wall (see Plate 17, figs. 1, 2). The relation of the orbital plate of 
the frontal (f}) to the orbitosphenoid (0.s.) is well seen here ; below, the bones of the 
palate are thick tracts, dividing on their inner edge into an upper and a lower plate to 
embrace, and protect, the nasopalatine canal (v.p.c.); these are, now, the ptery- 
goids (pg.). 
