THE TEMPOKAL BONES. 



129 



On the inferior surface of the petrous part, which is bounded in front by the 

 anterior border medially, the tympanic plate laterally, and behind by the posterior 

 border, the following structures are to be noted: Springing from and sur- 

 rounded by its sheath is the slender and pointed processus styloideus, the length 

 of which varies much. Projecting downwards and slightly forwards and medially, 

 it affords attachments for the stylo-glossus, stylo-hyoid, and stylo-pharyngeus 

 muscles, as well as the stylo-hyoid and stylo-mandibular ligaments. Just behind 

 it, and between it and the mastoid process, is the foramen stylomastoideum, which 

 lies at the anterior end of the mastoid groove, and transmits the facial nerve and 

 the stylo-mastoid artery. Just medial to the styloid process there is a deep, smooth, 

 excavated hollow, the fossa jugularis, which is converted into a foramen (jugular) 

 by articulation with the occipital bone. Behind and lateral to the fossa there is a 

 small quadrilateral surface 



Temporal surface 



Infra-temporal or zygomatic surface 



Canal for chorda tympani 

 Auditory tube 

 Carotid canal 



Tuberc 



Tuberculu 

 articulare 

 Mandibular 

 fossa 



Petro-tynipamc 

 exte^a-l fissure 

 Tympanic plate 

 Ext. acoustic meatus 

 Styloid. process 

 Sheath of styloid 

 process 



Mastoid process 



Mastoid notch for 

 digastric muscle 



Groove for 

 occipital artery 



Groove for 

 inferior 

 petrosal sinus 

 Aqueduct of cochlea 

 external orifice of) 

 nal for the 



nic nerve 

 'Jugular fossa 

 Canal for auricular 

 branch of vagus 



tympar 



Jugular surface 



of variable size, which is 

 united to the extremity of 

 the jugular process of the 

 exoccipital by a synchon- 

 drosis. Inside the fossa, on 

 its lateral part, or placed 

 on its lateral border, is the 

 opening of a small canal 

 (canaliculus mastoideus), 

 which passes laterally to 

 open into the canalis facialis, 

 and transmits the auricular 

 branch of the vagus, which 

 ultimately escapes through 

 the petro-mastoid fissure 

 (vide ante). In front of 

 the iuerular fossa and separ- Petro-mastoid fissure 



Stylo-mastoid 



ated from it by a sharp foramen 



crest, and just medial to the 

 tympanic plate, is the circu- 

 lar opening of the inferior 

 orifice of the canalis caroti- 

 cus (carotid canal). Directed 

 at first upwards, this canal 

 bends at a right angle and 

 turns for wards and medially, 

 lying parallel to the anterior 

 angle ; reaching the anterior 

 part of the apex of the bone, 

 it opens in front by an 

 oblique ragged orifice. 

 Through the canal the internal carotid artery, accompanied by a plexus of 

 sympathetic nerves, passes into the cranium. On the ridge of bone separating the 

 jugular fossa from the carotid canal is the opening of the canaliculus tympanicus, 

 through which the tympanic branch of the glosso - pharyngeal nerve passes to 

 reach the tympanum. Within the orifice of the carotid canal other small openings 

 (canaliculi carotici tympanici) may be noticed which afford passage to the tympanic 

 branches of the internal carotid artery and carotid sympathetic plexus.. Occupy- 

 ing the interval posteriorly and medially between the jugular fossa and the carotid 

 canal is a V-shaped depression on the floor of which and close to the posterior 

 border is the orifice of the apertura externa aquaeductus cochleae (aqueduct of 

 the cochlea). In the fossa is lodged the petrous ganglion of the glosso-pharyngeal 

 nerve, and the aqueduct transmits a tubular prolongation of the dura mater, 

 which forms a channel of communication between the perilymph of the cochlea 

 and the subarachnoid space. A small vein also passes through it. In front 

 of and medial to the orifice of the carotid canal the inferior surface of the 



9 



F;G. 138. THE RIGHT TEMPORAL BONE SEEN FROM BELOW. 



The squamo-zygomatic part is coloured blue ; the petro-mastoid, red. 

 The tympanic portion and styloid process are left uncoloured. 



