BONES OF THE FACE THE MAXILLA 63 



the external opening of the facial canal, through which the facial nerve emerges. The 

 bulla ossea is a considerable eminence situated centrally; it is thin walled and 

 incloses a cavity which is part of the tympanum. The muscular process (Processus 

 muscularis)'- is a sharp spine which projects downward and forward from the an- 

 terior part of the base; it gives origin to the tensor and levator palati muscles. 

 Lateral to the root of the preceding is the small petrotympanic fissure (Fissura 

 petrotympanica) for the passage of the chorda tympani nerve. The osseous 

 auditory or Eustachian tube (Tuba auditiva ossea) is a semicanal at the medial 

 side of the root of the muscular process; it leads to the tympanum. At the medial 

 side of the preceding is the slit-like orifice of the petrosal canal, which communi- 

 cates with the facial canal. 



The apex projects upward and backward between the squamous temporal and 

 the occipital bone. 



Development. — The squamous temporal develops in membrane. The pe- 

 trous temporal may be regarded as consisting of petro-mastoid and tympanic parts. 

 The latter includes the external acoustic process, the bulla ossea, and the muscu- 

 lar process; it is developed in membrane. The petro-mastoid is developed in the 

 cartilaginous ear capsule. Its petrous part consists of very dense bone which con- 

 tains the labyrinth or internal ear and forms the medial wall of the tympanum. 



The auditory ossicles and the interior of the petrous temporal bone are described in the 

 section on the organ of hearing. 



The temporal canal (Meatus temporalis)^ is a continuation of the transverse 

 groove which extends laterally from the base of the tentorium osseum. It is 

 directed downward, forward, and somewhat outward, and opens externally in front 

 of the root of the acoustic process. It is bounded by the squamous temporal 

 laterally, the petrous behind, and the parietal in front and medially. Several 

 foramina open from it into the temporal fossa. It contains a large vein (Vena 

 cerebralis dorsalis), the continuation of the transverse sinus of the dura mater. 



The foramen lacerum (basis cranii) is a large, irregular opening in the cranial 

 base, bounded medially by the basilar part of the occipital bone, laterally by the 

 petrous temporal, and in front by the temporal wing of the sphenoid. It consists 

 of a large anterior part (Foramen lacerum anterius), and a narrow posterior part 

 (Foramen lacerum posterius). It transmits the internal carotid artery, the middle 

 meningeal artery, the mandibular, ninth, tenth, and eleventh cranial nerves, and 

 the ventral cerebral vein. 



In the fresh state the foramen is occupied by a dense fibrous membrane which is perforated 

 by apertures for the various structures transmitted. Thus there are three openings in front for 

 the internal carotid artery, the mandibular nerve, and the middle meningeal artery; these are 

 named (from within outward) the foramen caroticum, ovale, spinosum. 



(B) BONES OF THE FACE 



The bones of the face (Ossa faciei) are the maxilla, premaxilla, palatine, 

 pterygoid, nasal, lacrimal, malar, dorsal turbinate, ventral turbinate, vomer, mandi- 

 ble, and hyoid. The last three are single, the others paired. 



The MAXILL.E 

 The maxillae are the principal bones of the upper jaw and carry the upper 

 cheek teeth. They are situated on the lateral aspect of the face, and articulate 

 with almost all of the facial bones and the frontal and. temporal also. For descrip- 

 tion each may be divided into a body and two processes. 



1 This has been termed the styloid process. It is not the homologue of the styloid proc- 

 ess of man. 



2 This is also known as the parieto-temporal canal. 



