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Questions and Answers, The Skull
1. Name the skull bones that make up the external bones of the cranium, the internal bones of the cranium, the bones of the ear, the external bones of the face, and the internal bones of the face.
External bones of the cranium:
Parietal bones (2)
Dorsolateral walls of cranium
Interparietal bones (2)
Dorsal midline
May fuse together
Occipital bone (1)
Base of skull
Spinal cord exits skull
Forms a joint with C1 (atlas)
Site of foramen magnum
Site of occipital condyles
Temporal bones (2)
Ventral to parietal bones
Forms lateral walls of the cranium
Contain middle and inner ear structures
Form tempromandibular ear structures
Form temporomandibular joints with mandible
Frontal bones (2)
Forehead region
Rostral to parietal bones
Form rostrolateral cranium and part of orbit
Frontal sinus
Corneal process of frontal bone
Internal bones of the cranium:
Sphenoid bone (1)
Forms ventral part of pituitary fossa
Splenoidal sinus
Ethmoid bone (1)
Rostral to sphenoid bone
Contains cribiform plate (related to smell)
Ethmoidal sinus
The external bones of the face:
Incisive bones (2)
Most rostral face bones
Home of upper incisors
Nasal bones (2)
Bridge of nose
Considerable variety in size and shape
Maxillary bones (2)
Upper jaw holds
Upper canine teeth
Cheek teeth
Maxillary sinuses
Hard palate
Lacrimal bones (2)
Two small bones that form the medial rtion of the orbit
Lacrimal sac (tears)
Zygomatic bones (2)
The internal bones of the face:
Palatal bones (2)
Form caudal part of palate
Nasal Turbinates (4)
Petrygoid bones (2)
Vomer bone (1)
The INTERNAL bones of the ear:
The very important pairs of ear bones are hidden away in the middle ear.
The following are known as ossicles
Mallus or Hammer (2)
Incus or Anvil (2)
Stirrup or Stapes (2)
2. In which skull bones are each of the
following structures found?
The cribiform plate, the external acoustic meatus, the foramen magnum,
the frontal sinus, the lacrimal sac, the lower teeth, the pituitary fossa,
the upper incisor teeth, the upper cheek teeth.
Cribiform plate—Ethmoid bone
The cribiform plate is the sievelike area of the ethmoid bone through
which the many branches of the olfactory nerve pass from the upper portion
of the nasal cavity to the olfactory bones of the brain.
External acoustic meatus—Temporal
bone
The external acoustic meatus is the only ear structure visible from the
outside. The eam is Is the bony canal that leads into the middle and inner
ear canvities. In the living animal it contains the external ear canal.
By looking into the eam we can see the middle ear cavity. Ventral to the
external acoustic meatus on each side is the concave articular joint surface
that receives the condyle of the mandible to form the TMJ. These articular
surfaces are located on the ventral surfaces of each of the temporal bones.
Foramen magnum—Occipital bone
A large hole, the foramen magnum, is in the center of the of the occipital
bone; this is where the spinal cord exits the skull. On the other side
of the foramen magnum are the occipital condyles, articular surfaces that
join with the first cervical vertebra, called the atlas, to form the atlantoocipital
joint, which is the joint that connects the head with the neck.
Frontal sinus—Nasal bone
The frontal bones form the forehead region of the skull. They are located
just rostral to the parietal bones and they form the rostrolateral portion
of the cranium and a portion of the orbit, which is the concave socket
that holds the eye. A large paranasal sinus, the frontal sinus, is contained
within the frontal bone. In horned cattle breeds, the cornual process
of the frontal bone is the horn around which the horn develops. This process
is hollow, and communicates with the frontal sinus.
Lacrimal sac—Lacrimal bone
The two small lacrimal bones form part of the medial portion of the orbit
of the eye and house the lacrimal sacs, which are part of the tear drainage
system of the eye.
Mandible—Lower Teeth
The mandible is the lower skull, the only movable skull bone. The mandible
houses all of the lower teeth. It is usually referred to as a single bone,
but in dogs, cats, and cattle, the two halves of the mandible are separate
bones joined by a cartilaginous mandibular symphysis at the rostral end.
Sphenoid bone—Pituitary Fossa
A single sphenoid bone forms the ventral part of the cranium and contains
a depression, the pituitary fossa, that houses the pituitary gland, which
is an important endrocrine, or hormone producing gland. The sphenoid bone
is located rostral to the occipital bone. If removed from the skull and
examined, this bone looks like a bat with its wings and legs extended.
This is why some refer to it as the bat bone. The sphenoid bone of most
animals contains a paranasal sinus called the sphenoidal sinus.
Upper incisor teeth—Incisive bone
The two incisive bones, sometimes called the premaxillary bones, are the
most rostral (forward) skull bones. In all common domestic animals except
ruminants, such as cattle, sheep, and goats, the incisive bones house
the upper incisor teeth. Our ruminant friends (if you want to call them
this) do not have upper incisor teeth, rather they have a hard dental
pad. It is quite difficult to make dentures for these critters because
they spit them out and step on them. When placed back
in the mouth, these fine animals then develop dental rot.
Upper Cheek Teeth—Maxillary bone
The two maxillary bones make up most of the upper jaw. The incisive bones
make up the rest. The maxillary bones house the upper canine teeth, all
of the cheek teth, (premolars and molars) and the maxillary sinuses. Along
with the palatine bones, the maxillary bones form the hard palate, which
is the bony separation between the mouth and the nasal cavity that we
call the roof of the mouth. The maxillary bones form the rostral (forward
portion of the hard palate, and the palatine bone for the caudal (rear)
portion.
3. Which would likely be a greater threat
to animal’s well being, a fracture of the mandible or a fracture
of the occipital bone. Why?
The fracture of the occipital bone would be a greater threat.
Injuries to this bone are serious. Because of its location and the vital
structures that it encloses. It is where the spinal cord exits the skull
and it is also the skull bone that articulates (forms a joint) with the
first cervical neck vertebrae.
The Skull