THE TEMPORAL BONE 87 



carotid canal from the jugular fossa. (6) A small foramen on the wall of the 

 jugular fossa, for the passage of the articular branch of the vagus (Arnold's) nerve. 

 (7) Behind the jugular fossa a smooth, square-shaped facet, the jugular surface; 

 it is covered with cartilage in the recent state, and articulates with the jugular 

 process of the occipital bone. (8) The stylomastoid foramen (foramen stylo- 

 mastoideum), a rather large orifice, placed between the styloid and mastoid pro- 

 cesses; it is the termination of the aquaeductus Fallopii, and transmits the facial 

 nerve and stylomastoid artery. (9) The auricular fissure (fissura tympanomas- 

 toidea), situated between the tympanic plate and mastoid process, for the 

 passage of the auricular branch of the vagus nerve. This fissure is the 

 external opening of the canaliculus mastoideus, which passes to the aqueduct of 

 Fallopius. 



Borders. The antero-superior border (angulus superior pyramidis), the longest, 

 is grooved for the superior petrosal sinus, and has attached to it the tentorium 

 cerebelli; at its inner extremity is a semilunar notch, upon which the fifth 

 nerve lies. 



The postero-inferior border is intermediate in length between the antero-superior 

 and antero-inferior. Its inner half is marked by a groove, which, when completed 

 by its articulation with the occipital, forms the channel for the inferior petrosal 

 sinus. Its outer half presents a deep excavation, the jugular fossa (fossa jugularis), 

 which, with a similar notch on the occipital, forms the foramen lacerum posterius. 

 A projecting eminence of bone occasionally stands out from the centre of the notch, 

 and divides the foramen into two parts. 



The antero-inferior border is divided into two parts an outer, joined to the 

 squamous portion by a suture, the remains of which are distinct; an inner, free, 

 articulating with the spinous process of the sphenoid. At the angle of junction 

 of the petrous and squamous portions is seen the opening of the canalis musculo- 

 tubarius. The antero-inferior border is free and affords attachment to the 

 Tensor tympani and Levator palati muscles. 



The Tympanic Portion (pars tympanica). The tympanic portion is placed in 

 front of the anterior surface of the petrous portion; its most internal part is 

 narrow and forms the anterior wall of the Eustachian canal. Externally it 

 broadens out and has an antero-inferior and a postero-superior surface, an 

 antero-superior, an antero-inferior, and an external border. The antero-inferior 

 surface looks forward and downward and forms the posterior part of the glenoid 

 fossa. The postero-superior surface forms the anterior wall of the external audi- 

 tory canal. From this surface there continues on to the anterior part of the 

 mastoid portion a U-shaped process, with its concavity upward; this process 

 shares in forming the inferior and posterior wall of the external auditory canal. 

 Between the upturned part of the U-shaped process and the mastoid is a foramen 

 (fissura tympanomastoidea) transmitting the tympanic (auricular nerve of Arnold) 

 branch of the vagus. In the concavity of this process is a furrow (sulcus tym- 

 panicus], in which is placed the tympanic membrane (membrana tympani), like a 

 mirror in its frame. The antero-superior border fuses with the middle zygomatic 

 root. Internally, this border is continuous wifh the upper border of the narrow 

 part of the bone, and is separated from the squamous portion of the bone by 

 the Glaserian fissure and a small part of the tegmen tympani. The antero- 

 inferior border is thin internally; externally it divides into two laminae and 

 ensheaths the root of the styloid process hence the name vaginal process given 

 to this border. The external border is free and rough, and has attached to it the 

 cartilaginous part of the ear. 



The glenoid fossa (fossa mandibularis) is a considerable hollow formed by the 

 squamous part of the temporal, and behind by the tympanic bone. The part of 

 the fossa formed by the squamous portion is covered with cartilage and articulates 



