DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 45 
and between them and the condyle (0c.c.) there is a very inconspicuous paroccipital 
tract. The exoccipital and supraoccipital (e.0., s.o.) are seen in the midst of large 
tracts of solid cartilage. 
It is impossible to look at the end view (fig. 4) without being reminded of low 
Ichthyopsidan types of skull ; the cartilage is as solid as in them, and the osseous 
centres are mere patches in it. The general form of the occipital end-wall is trans- 
versely oval ; it overhangs a little above (see fig. 3), and then curls over, above, where 
the bony centre (s.0.)—single now, but undoubtedly double once—is somewhat 
trilobate. This supraoccipital centre is thus like a sessile leaf with a trilobate upper 
outline, and a concave petiolar attachment ; this is the lower margin over the foramen 
magnum (fim.). What looks in the side view (fig. 3) like a large epiotic swelling is, 
in reality, seen here to be the thick convex edge, right and left, of the great supra- 
occipital shield. Here we see the whole line of demarcation between the auditory 
capsule and the back wall of the skull proper, converted into an arcuate chink, which 
becomes a triangular recess, below Outside this, the epiotic and opisthotic regions 
(op.)—to the latter of which the epihyal (e.hy.) is fused, and through which the 
facial nerve (VII.) passes—is but a narrowish convex, lateral tract, thinning out helow, 
where it flanks a very indefinite paroccipital tract (p.oc.). Inside that tract, and over 
and within the condyle (oc.c.), we see the orbicular, exoccipital (¢.0.), only one-tenth 
the size of the once double upper bony tract (s,0.), 
Like the rest of the skull the occipital basal margin and condyles are a very wide 
structure, the bony basioccipital does not reach the foramen magnum ; this passage is 
lower than in Tatusia (Plate 6, fig. 4), it inclines upwards and backwards (see figs. 1 
and 3), The parietals (p.) and squamosals (sq.) are hardly seen in this view. 
The mandible (figs. 3, 34) has the same general shape as in Tatusva, but it is heavily 
built, and not at all like the elegantly slight structure seen in the other kind; the 
teeth also run further forwards, and are larger. Altogether this type is further from 
the Anteaters than the others, and on the whole less modified from the average 
Mammalian type. 
A little cartilage is still seen in the coronoid and angular processes as well as in 
the articular; MecKkev’s cartilage (mk.) is still quite perfect. The malleus (figs. 34 
and 6, ml.) is unlike that of Tatusia, the head is more solid, and the pesterior angular 
process is more distinct, but high up, almost close to the articular condyle. The 
manubrium forms an acute angle with the main bar instead of being parallel with it, 
“elbow ” low down; it is also longer, and is dilated at its end. 
and having its 
The small, hooked ectosteal plate has only just begun to graft itself on the under 
face of the malleus. The incus (7.), which is quite unossified, is like that of Tatusva, 
and so is the stapes (s¢.) ; it also shows a small “interhyal” (7.4y.) in the tendon of the 
stapedius muscle (st.m.). The hyoid arch is quite normally Mammalian, and not like 
that of Tatusia; the epihyal (figs. 4 and 5, e.hy.) lingers on as part of the general 
arch, which is thus tied to the skull; the partly ossified upper ceratohyal (c.hy.), not 
