The =occipital bone= is situated in the lower part only of the posterior
surface of the skull, and is separated from the highest part (the
frontal eminence) by the parietal and interparietal bones. The
supraoccipital, interparietals, and parietals fuse before birth or soon
after, and the mass so formed is separated from the lateral parts of the
occipital bone by a transverse suture in the skull of the calf. Above
this suture is a central tuberosity, to which the ligamentum nuchæ is
attached, and the surface on either side is depressed and rough for
muscular attachment. Below the suture the bone is much wider than that
of the horse. The foramen magnum is wide, so that the condyles are
further apart except below. The paramastoid processes are short and wide
and are bent inward. Two constant foramina are found in the condyloid
fossa; the anterior one is the hypoglossal, the other (sometimes double)
conducts a vein from the =condyloid canal=. The latter passes upward
from a foramen on the inner side of the condyle and opens into the
parieto-temporal canal. The cranial surface of the supraoccipital
presents a central depression, and above this is a variable but never
very pronounced eminence, which corresponds to the tentorium osseum of
the horse. On either side is a groove leading to the parieto-temporal
canal. The basilar process is short and wide; its cranial surface is
deeply concave, and the internal spheno-occipital crest is prominent.
Two large tubercles below mark the junction with the sphenoid. The
foramen lacerum is short and very narrow. In the adult animal the bone
is excavated to contain an air-cavity which is regarded as a part of the
frontal sinus.
The =sphenoid bone= is short. The cranial surface of the body presents a
deep sella turcica, in front of which it rises abruptly. The high
anterior part bears a central ridge (Rostrum sphenoidale), which joins
the crista galli of the ethmoid. Two foramina occur on either side. Of
these, the large anterior one is equivalent to the foramen rotundum,
lacerum orbitale, and patheticum of the horse. The posterior one is the
=foramen ovale=, which transmits the inferior maxillary nerve. The
orbital wing is thick and is overlapped by the frontal in such manner as
to appear externally to divide into two branches; the anterior part
joins the ethmoid close to the sphenopalatine foramen, and contains a
small sinus which communicates with an ethmoidal meatus. The temporal
wing is small, but forms a prominent thick pterygoid crest. The
pterygoid process is wide, and the pterygoid or alar foramen is absent.
The sphenoidal sinus is absent in the calf and small in the adult; it
communicates by one or two small openings with an ethmoidal meatus, and
so with the nasal cavity.
[Illustration: