DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
75 
other edentulous types, as for instance in a remarkable Neotropical Passerine Bird— 
Phytotoma rara (Trans. Zool. Soc., vol. 10, plate 46, figs. 8-10); and in a gigantic 
Toad ( Bufo agua, Phil. Trans., 1881, Plate 36, fig. 2) from the same region, whose 
palatines (normally edentulous in existing Anura) show signs of an old tooth-surface 
in the form of sharp osseous denticulations. 
In this slender mandible, decurved like the snout end of the upper jaw, the coronoid 
process {cr.p.) is a good wide hook, separated from the round condyloid process (<cd.p .), 
with its clearly marked neck, by a large semicircular notch; a shallow notch separates the 
latter from the less marked angular process (< ag.p .), which is slightly incurved. The 
inner face of the ramus (fig. 3a) shows tracts or regions of bone that correspond most 
accurately with the coronoid and splenial bones of the Oviparous Yertebrata; the 
rapid ossification of the ramus from the main bone, or dentary, does not allow of 
distinct centres for these parts ; at least, as far as I have seen, they are only partially 
distinct. 
The end view of this skull (fig. 4) is as important as the other aspects, which have 
to be corrected, visually, by this. The fundus of this flask-shaped skull is subcircular 
and gently convex ; the perfect semicircle, above, is finished in its outline by the 
deep parietals (p.) ; the rest of the outline is made more irregular than it would be by 
the appearance, in the distance, of the hinder swellings of the tympanies ( a.ty .). The 
supraoccipital (s.o.) is reniform, with a concentric muscular ridge, but the lower edge, 
besides its “ hilus” over the large, nearly circular foramen magnum ( fm .), is notched, 
right and left, by the squared upper end of the exoccipitals (e.o.) ; the upper and 
outer junction of these bones is sinuous, the outer and lower margin fitting against 
the opisthotic (op.) is rounded. A notch separates the outer lobe, with its thick par- 
occipital edge, from the reniform condyle, and between the right and left condyles 
the basioccipital comes into view. Here we see the extraordinary development of the 
“ basipterygoids ” of the basioccipital ( b.pg .) like those of the Unau (Plate 9, fig. 1), 
but larger, and carrying the ends of each pterygoid bone (pg.). The lower face of each 
pterygoid is flat, but oblique, the outside being the deeper part; the interspace 
between the two bones is not greater than the width of each; this is floored by a strong- 
membrane, and thus the circular hind part of the naso-palatine canal {n.p.c.) is 
completed, a little in front of the foramen magnum. A membranous interspace is seen 
between each tympanic and the opisthotic {a.ty., IX., X.); outside the broad outer 
opisthotic part we see the hind margin of the narrow squamosal (sq.), and over the 
tympanic the epihyal (e.hy.), and right and left in this region the nerve passages for 
the facial, glossopharyngeal, vagus, and hypoglossal (VII., IX., X., XII.). 
The external views (figs. 1-3) were taken from the smaller dry skull, with the help 
of the larger spirit-specimen; the sectional views (figs. 7 and 8), the hyoid (fig. 6), and 
* The embryology of the Myrmecophagidse and of the Manidae would possibly show us rudimentary 
teeth in both families. 
L 2 
