82 PROF. W. K. PARKER ON THE STRUCTURE OF 
behind the co-adapted upper spurs, the base of the cartilaginous orbital septum (p.s, 
p.é) is seen, with a widening membranous space on each side of it as the pterygoids 
diverge backwards. These bones (fig. 2, pg) are one half longer than the palatines, and 
they pass obliquely inside these bones, and then send out a triangular spur close 
behind the suture. Then they seem to lessen to one half their front width; but this 
is due to a change in the direction of the expanded part from horizontal to vertical. 
Their hinder part is the broader by far, and is a large reniform lobe (fig. 1), which is 
lowest opposite the ascending jugal bone (j), and then rises to be attached by ligament 
to the quadrate (q). Instead of passing within that bone, it comes short of it by a definite 
space. Behind the sinuous inner margin of the flat part, the pterygoid has an oblique 
facet of cartilage, which lies obliquely over and outside a similar facet on the “ basi- 
pterygoid” (b.pg.). Attached to the outer spur of the pterygoid, and wedged between 
it and the jugal process of the maxillary, is a four-cornered oblique plate of bone, one 
third the size of the palatine ; this is the “ transpalatine” (¢. pa). This bone forms, with 
the pterygoid, the hind boundary of a large oval palatine fenestra, the outer wall of 
which is formed by the maxillary and the inner by the palatine. 
The investing bones of the lower jaw (Plate XVI. fig. 1, and Plate XVII. fig. 1) 
are a dense well-compacted series of splints. The dentary (d) is much the largest of 
these, and occupies nearly all the outer face of the jaw and carries all the teeth; it is 
seen, above and below, on the inner side. On the outside, within and behind the 
dentary, the articulare (a7) is invested with the angulare (aq), a small style; the supra- 
angulare (s.ag), is a wider plate, which overlaps the jaw and is seen most on the inner 
side (Plate XVII. fig. 1). On the inner side, in turn overlapping the supra-angulare, we 
see the large four-cornered coronoid (cr), whose upper angle forms the crest or coronoid 
part of the jaw ; it bends down upon the supra-angulare behind, the articulare below, and 
the dentary and splenial in front. The latter bone (Plate XVII. fig. 1, sp) is a thin 
lath of bone, widest in front, where it reaches the chin, and narrowest behind; it 
hides the upper edge of Meckel’s cartilage (mx). 
B. The Endocraniwn. 
The inner part of the skull is composed of membrane, cartilage, and bone; the hind 
part is largely ossified, but keeps most of the subdividing synchondroses. The fore part 
is cartilaginous, with subcentral calcifications running in certain lines between the orbits ; 
the ethmoidal and nasal regions are free even from this deposit (Plate XVII. figs. 1-4). 
In front of the postcranial roof there is a long pyriform fontanelle; and the tract 
between the eye and ear is largely membranous. ‘This arises from the arrest of the 
alisphenoid (a/.s) ; the orbitosphenoidal tracts are very narrow, and become mere lips to 
the orbital septum, only spreading again in the cribriform region, where the olfactory 
