BONES OF THE FACE 57 



The anterior surface looks iijiward and forward. The outer part articulates 

 with the parietal bone and the inner part faces into the cerebral fossa of the cranium. 

 A sharp border, the petrosal crest (Crista petrosa), separates this surface from the 

 inner one. 



The posterior surface joins the lateral part of the occii)ital bone. 



The base forms the outer Ijoundary of the foramen laccn-um Ijasis cranii. It 

 is very irregular and presents a number of important features. The hyoid process 

 is a short rod which projects downward and forward below the base of the external 

 auditory process, inclosed in a bony tube ; it is connected by a bar of cartilage with 

 the hyoicl bone. The stylo-mastoid foramen is situated between the root of the 

 hyoid process and the mastoid process; it is the external opening of the facial canal, 

 through which the facial nerve emerges. The bulla ossea is a considerable emi- 

 nence situated centrally; it is thin-walled and incloses a cavity which is part of the 

 tympanum. The muscular process' is a sharp spine which projects downward 

 and forward from the anterior part of the base; it gives origin to the tensor and 

 levator ]ialati muscles. External to the root of the preceding is the small petro- 

 tympanic or Glaserian fissure (f^issura petro-tympanica) for the passage of the 

 chorda tympani nerve. The osseous Eustachian tube is a semicanal at the inner 

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

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

 with the facial canal. 



The apex projects upward and backward between the scjuamous temporal and 

 the occipital bone. 



Development. — The petrous temporal may be regarded as consisting of petro- 

 mastoid and tympanic parts. The latter includes the external auditory process, 

 the bulla ossea, and the muscular process; it is developed in membrane. The 

 petro-mastoicl is developed in the cartilaginous ear capsule. Its petrous part 

 consists of verj^ dense bone which contains the labyrinth or internal ear and forms 

 the inner wall of the tympanum. 



The parieto-temporal canal (Meatus temporalis) is a continuation of the trans- 

 verse groove which extends outward from the base of the tentorium osseum. It 

 is directed downward, forward, and somewdiat outward, and opens externally in 

 front of the root of the auditory process. It is bounded by the squamous temporal 

 externally, the petrous behind, and the parietal in front and internally. 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 (Foramen lacerum et jugulare) is a large 

 irregular opening in the cranial base, bounded internally l)y the basilar part of the 

 occipital bone, externally by the petrous temporal, and in front by the temporal 

 wing of the sphenoid. It consists of a large anterior part (Foramen lacerum an- 

 terius), and a narrow posterior part (Foramen lacerum posterius s. jugulare). 

 It transmits the internal carotid artery, the middle meningeal artery, the mandi- 

 bular, ninth, tenth, and eleventh cranial nerves, and the inferior 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 

 (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, Superior Turbinal, Inferior Turbinal, Vomer, 



Mandible, and Hyoid. The last three are single, the others paired. 



1 This is commonly termed the styloid process. It is not the homologue of the styloid process 

 of man. 



