_13_, Basi-occipital; _13″_, paramastoid or styloid process; _13‴_,
occipital condyle; _24′_, incisor teeth; _28_, body of mandible;
_31_, condyle of mandible; _32_, ventral tubercle of atlas. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The =frontal bones= are very extensive, forming about one-half of the
entire length of the skull, and all of the roof of the cranium. The
posterior borders form with the parietals a large central =frontal
eminence= (Torus frontalis), the highest point of the skull. At the
junction of the posterior and the lateral borders are the =processus
cornu= or “horn-cores,” for the support of the horns. These processes
are of elongated conical form, and vary greatly in size, length,
curvature, and direction. The external surface is rough and porous,
marked by numerous grooves and foramina; in the fresh state they are
covered by the matrix of the horns. The base has a constriction, the
neck. The interior is excavated to form a number of irregular
intercommunicating spaces, divided by bony septa, and communicating with
the frontal sinus. In the polled breeds these processes are absent, the
skull is narrower in this region, and the frontal eminence more
pronounced. The supraorbital process is situated about half-way between
the anterior and posterior margins; it is short and joins the frontal
process of the malar bone. The supraorbital foramen (often double) is
situated about an inch inward from the root of the process; it is the
external orifice of the =supraorbital canal= (Canalis supraorbitalis),
which passes downward and forward into the orbit. The foramen is in the
course of the =supraorbital groove= (Sulcus supraorbitalis), which marks
the course of the frontal vein. The anterior ends of the naso-frontal
parts form a notch which receives the nasal bones, and sutural or
Wormian bones are often found at this junction (naso-frontal suture).
The orbital part is extensive; it is perforated behind by the orbital
opening of the supraorbital canal, and below by the ethmoidal or
internal orbital foramen. It does not articulate with the palatine, from
which it is separated by the orbital wing of the sphenoid. The temporal
part is also more extensive than in the horse. The frontal sinus is very
extensive, being continued into the parietals and occipital, and the
horn processes when present.
The =squamous= and =petrous parts= of the =temporal bone= fuse early—in
fact, union is nearly complete at birth. The squamous part is relatively
small. Its external surface is divided into two parts by the prominent
temporal crest, which is continuous with the parietal crest above and
turns forward below, ending at a tubercle above the external auditory
meatus. The part behind the crest faces backward, and is partly free,
partly united with the occipital. The area in front of the crest is
concave and enters into the formation of the temporal fossa; it is
perforated by foramina which communicate with the parieto-temporal
canal. The zygomatic process is much shorter and weaker than in the
horse, and articulates with the malar only. The condyle is convex in
both directions. The postglenoid process is less prominent, and behind
it is the chief external opening of the parieto-temporal canal. The
internal surface is almost completely overlapped by the parietal and
sphenoid. The petrous part proper is small, but the tympanic part is
extensive. The external auditory meatus is smaller than in the horse and
is directed outward. From it a plate projects downward and helps to
inclose the deep depression in which the hyoid process is placed. Behind
this plate is the stylo-mastoid foramen. The muscular process is large
and often bifid at its free end. The bulla ossea is large and laterally
compressed. It is separated from the occipital bone by a narrow opening
which is equivalent to part of the foramen lacerum basis cranii of the
horse. The parieto-temporal canal is formed entirely in the temporal
bone. The facial canal, on the other hand, is bounded partly by the
occipital bone.