The skull consists of, (1) an axial portion, the cranium,
enclosing the brain and forming an anterior continuation of the
vertebral column: (2) the olfactory capsules and the auditory
capsules, which are fused with the anterior and posterior ends
of the cranium respectively : (3) the bony framework of the
jaws: and (4) the hyoid apparatus.
In the skull the original cartilage, or chondrocranium, is not
so largely replaced by bone as in the vertebral column, large
tracts of unossified cartilage persisting in the adult. Besides
the cartilage-bones the skull is further strengthened by the
addition of numerous membrane-bones.
1, The Cranium is an unsegmented cartilaginous tube, whose
cavity forms the anterior part of the neural canal,
and lodges the brain. The roof of the tube is imper-


54 THE SKELETON OF THE FROG.
fect, there being one large. anterior fontanelle, and
two smaller posterior fontanelles, which are closed by
membrane only. In the cartilage are developed carti-
lage-bones, and around it membrane-bones.
To study the cranium satisfactorily, the membrane-bones should
be stripped from one of the skulls you have prepared for yourself.
a. Cartilage-bones of cranium.
i. The exoccipitals are two irregular bony masses at
the sides of the posterior end of the skull. They
almost completely surround the foramen magnum
or entrance to the cranial cavity ; and bear on
their posterior surfaces the occipital condyles,
two oval convex processes which articulate with
the first vertebra or atlas.
Fig. 9. The frog’s skull, from the ventral surface.
a, parasphenoid : c, columella: e, exoccipital: fp, frontoparietal :
m, maxilla: nm, vomer: o, pro-otic: p, pterygoid: pa, palatine:
pm, premaxilla : g, quadratojugal : se, sphenethmoid.
