THE TEMPORAL BONE 73 



bule, is an irregular opening, the fossa subarcuata, the remains of the floccular fossa, a con- 

 spicuous depression in the fcEtal bone. In the adult the depression usually lodges a process of 

 dura mater and transmits a small vein, though in some bones it is almost obliterated. 



The anterior surface of the pyramid, sloping downward and forward, forms 

 the back part of the floor of the middle fossa of the cranium. 



Upon the anterior surface of the pyramid will be found the following points of interest, 

 proceeding from the apex toward the base of the pyramid:— (1) a shallow trigeminal im- 

 pression for the semilunar (Gasserian) ganglion of the trigeminal nerve; (2) two small grooves 

 running backward and laterally toward two small foramina overhung by a thin osseous Up, the 

 larger and medial of which, known as the hiatus canalis facialis, transmits the great superfi- 

 cial petrosal nerve and the petrosal branch of the middle meningeal artery, whilst the smaller 

 and lateral foramen is for the small superficial petrosal nerve; (3) behind and lateral to these 

 is an eminence — the eminentia arcuata — best seen in young bones, corresponding to the su- 

 perior semicircular canal in the interior; (4) still more laterally is a thin transulcent plate of 

 bone, roofing in the tympanic cavity, and named the tegmen tympani. 



Fig. 94. — The Foramina in the Fundus of the Left Internal Auditory Meatus of a 



Child at Birth (f). (Diagrammatic.) 



Superior fossa 



Foramen singulare 



^^ Entrance to the facial canal 



Superior cribriform area- 



Transverse crest 



Middle cribriform area TT^^ #^^I_L__ Orifice of the canal of the modiolus 



Spiral cribriform tract 



I 

 Inferior fossa 



The inferior or basilar surface of the pyramid is very irregular. At the apex 

 it is rough, quadrilateral, and gives attachment to the tensor tympani, levator 

 veil palatini, and the pharyngeal aponeurosis. Behind this are seen the large 

 circular orifice of the carotid canal for the transmission of the carotid artery and 

 a plexus of sympathetic nerves, and on the same level, near the posterior border, 

 a small three-sided depression, the canaliculus cochleae, which transmits a small 

 vein from the cochlea to the internal jugular. Behind these two openings is the 

 large elliptical jugular fossa which forms the anterior and lateral part of the 

 bony wall of the jugular foramen, in which is contained a dilatation on the 

 commencement of the internal jugular vein; on the lateral wall of the jugular 

 fossa is a minute foramen, the mastoid canaliculus, for the entrance of the 

 auricular branch of the vagus (Arnold's nerve) into the interior of the bone. 

 Between the inferior aperture of the carotid canal and the jugular fossa is the 

 sharp carotid ridge, on which is a small depression, the fossula petrosa, and at the 

 bottom of this a minute opening, the tympanic canaliculus, for the tympanic 

 branch of the glosso-pharyngeal or Jacobson's nerve, and the small tympanic 

 branch from the ascending pharyngeal artery. Behind the fossa is the rough 

 jugular surface for articulation with the jugular process of the occipital bone, on 

 the lateral side of which is the prominent cylindrical spur known as the styloid 

 process with the stylo-mastoid foramen at its base. The facial nerve, and 

 sometimes the auricular branch of the vagus, leave the skull, and the stylo-mas- 

 toid artery enters it by this foramen. Running backward from the foramen are 

 the mastoid and occipital grooves already described. 



The tympanic surface of the pyramid, forming the medial and posterior 

 walls [paries labyrinthica] of the tympanic cavity, is shown by removing the 

 tympanic plate (fig. 91). It presents near the base an excavation, known as the 

 tympanic or mastoid antrum, covered by the triangular part of the squamous 

 below and behind the temporal line. The opening of the antrum into the 

 tympanic cavity is situated immediately above the fenestra vestibuli, an oval- 

 shaped opening which receives the base of the stapes; below the fenestra vestibuli 

 is a convex projection or promontory, marked by grooves for the tympanic plexus 

 of nerves and containing the commencement of the first turn of the cochlea. 

 In the lower and posterior part of the promontory is the fenestra cochleae, closed 

 in the recent state by the secondary membrane of the tympanum. Running 

 downward and forward from the front of the fenestra vestibuli is a thin curved 

 plate of bone [septum canalis musculotubarii], separating two grooves converted 



