ANATOMY OF HETERODONTUS: ENDOSKELETON 451 
wall is membranous (fig. 2). The olfactory cup or inside of the 
capsule communicates internally with the cranial cavity by the 
olfactory foramen, through which the first cranial nerve passes. 
At the free margin of the capsule there is a scroll-like nasal 
cartilage (n.c.1, fig. 2), which runs on the outer margin around 
the aperture of the capsule. Both the anterior and posterior 
ends of the cartilage recurve upon themselves medially so as to 
form a narrow ellipse, across which, from its antero-lateral third, 
a projection extends backward and inward, forming of the ellipse 
a figure 8. 
A second nodule of cartilage (n.c.2; not figured by Gegen- 
baur ’72 for H. philippi, pl. 16, fig. 2) is loosely attached to the 
anterior end of the first nasal cartilage. The attachment is 
made at its broader anterior end and its free tip extends backward 
to be connected by tissue with the deeper recurved anterior end 
of the first cartilage. 
In side view (fig. 3) the olfactory capsules occupy a position 
remote from the main part of the cranium. Projecting from the 
postero-lateral part of the cranium are the thick-walled auditory 
capsules (a.c.) which give protection to the organs of hearing. 
Between the auditory and nasal capsules is the large socket 
or orbit in which is located the eye. Overhanging the orbit 
is the broad supraorbital crest (s.o.) from the anterior part of 
which arises the preorbital process (pr.o.) and from the poste- 
rior, the post-orbital process (po.o.). The floor of the orbit ex- 
tends outward as the basal plate. Anterior to this plate and 
running between the orbit and the olfactory capsule is the 
elongated palatal fossa (pl.f.) previously noted in ventral view. 
Perforating the brain case in the orbit are numerous foramina 
through which nerves or blood vessels course between the brain 
on the one hand and the structures of the eye and the facial 
region on the other. Ventrally and a little in front of the middle 
of the orbit is a large opening, the optic foramen (f.J/), through 
which the optic nerve reaches the brain. Above and slightly 
anterior to the optic is a small trochlear foramen (f.JV) through 
which the fourth cranial nerve passes to the superior oblique 
muscle of the eye. Behind the optic foramen, and in the lower 
