Temporal bone

Ox

Temporal bone form part of the lateral walls of the cranium. They are situated between the occipital and the parietal behind, and the frontal dorsally and sphenoid ventrally and medially. Each consists of squamous and petrous parts, which are fused completely at birth.

Squamous temporal

• It has a body and zygomatic process.
• The external surface of the body is divided by the temporal crest into two parts.
• The crest is continuous with the parietal crest above, turns forward below ending in a tubercle, above the external acoustic meatus. This corresponds to the mastoid process (on the petrous part of the horse). The area in front of the crest is the temporal fossa and presents two or three foramina leading into the temporal canal. The area behind the crest is smaller and meets the occipital bone.
• The internal surface is overlapped by the parietal and sphenoid.
• The zygomatic process is wide behind and narrow in front. The anterior part of zygomatic process meets the zygomatic process of the malar to form the zygomatic arch.
• At its upper part it forms dorsally part of the temporal fossa and ventrally it presents an articular area-a condyle, a glenoid cavity and a postglenoid process-for articulation with the mandible.
• Behind the postglenoid process is the post glenoid foramen-the external opening of the temporal canal. This canal is formed by the opposition of squamous and petrous-temporal bones. This canal is a continuation of the groove mentioned in the squamous part of the occipital and its internal opening lies above and behind the petrous part of the petrous temporal bone. It contains the dorsal cerebral vein the continuation of the transverse sinus of the duramater.

Petrous temporal

• The petrous temporal is situated between the occipital behind and the squamous temporal in front. It consists of petrous and tympanic parts.
• Petrous part
  • The petrous part contains internal ear.
  • The medial face is smooth and forms the lateral wall of the cerebellar compartment of the cranial cavity.
  • It presents the internal acoustic (auditory) meatus for the VII and VIII cranial nerves.
  • The fundus of the meatus is divided by a crest into two fossae. In the superior one is the origin of the facial canal (aquaeductus Fallopius), which curves through the bone and opens externally at the stylomastoid foramen, it transmits the seventh cranial nerve.
  • The inferior fossa presents small foramina for the passage of the fibers of the eighth cranial nerve.
  • Behind the meatus and near the posterior margin of the surface is the slit-like opening of aquaeductus vestibuli covered by a scale of bone. Below it forms part of the cerebral compartment.
  • The petrosal crest separates these two surfaces.
• Tympanic part
  • The tympanic part is external and presents the following:
  • The external auditory process-a curved plate of bone projecting through a notch in the squamous temporal and encloses the external acoustic meatus.
  • Blow the external auditory process is a rod of bone- the hyoid process. This is connected by a bar of cartilage to the styloid cornu of the hyoid bone.
  • Between the hyoid and the paramastoid processes is the stylomastoid foramen-the external opening of the facial canal.
  • The bulla tympanica (auditory bulla) whose cavity forms part of the middle ear.
  • The muscular (styloid) process of the petrous temporal springs from below the bulla for muscular attachment.
  • Lateral to the root of this process is the petrotympanic (Glaserian) tissue for the chorda tympani nerve and medially is a groove or semicanal-the osseous eustachian tube (auditory tube).

Horse

• The squamous part is relatively larger. It presents a zygomatic and posterior triangular process.
• The zygomatic process meets not only the malar but also the supra-orbital process of the frontal.
• The posterior process springs from the posterior aspect of the body and presents a temporal crest on its lateral face. Its medial surface forms the outer boundary of the parieto-temporal canal.
• The parietal bone takes part in the formation of the temporal canal (parieto-temporal canal). There is a well developed mastoid process between the squamous-temporal and the paramastoid processes.
• The stylo mastoid foramen is between the hyoid and the mastoid processes. The auditory bulla is smaller.

Dog

• The parts of the temporal bone fuse early.
• The zygomatic process is strongly curved.
• Its anterior part is beveled ventrally and articulates extensively with the corresponding process of malar.
• The articular area is represented by a transverse groove and it extends upon the front of the large postglenoid process.
• A distinct mastoid process is present.
• The external acoustic meatus is very short and wide so that in the dry skull one can see into the tympanum.
• The bulla tympanica is very large and rounded and smooth, its medial side is united to the basilar part of the occipital bone.
• Above this junction and roofed in by the union of the petrous parts and the basioccipital is the petrobasilar canal; this transmits a vein from the floor of the cranium to the foramen lacerum posterius. The latter opens into a depression behind the tympanic bulla. It transmits the 9th, 10th and 11th cranial nerves.
• The carotid canal branches off from the petro-basilar, passes forward lateral to it through the medial part of the bulla tympanica and opens in front of the carotid foramen; it transmits the internal carotid artery. The eustachian opening is immediately lateral to the carotid foramen. The muscular and hyoid processes are very rudimentary.
• The petrosal crest is sharp and prominently projects into the cranial cavity. The medial surface presents a deep floccular fossa above the internal acoustic meatus. The anterior angle is perforated by a foramen for the trigeminal nerve.

Fowl

• The squamous temporal lies on the lateral aspect of the cranium. It presents the supra orbital and the zygomatic process.
• The former is fused to that of the frontal; it furnishes a facet for the quardrate bone.
• The petrous temporal is concealed by the adjacent bones. It forms the floor of the tympani cavity and a part of the facet for the quadrate bone.