84 



SPECIAL ANATOMY OF THE SKELETON 



The Petrous Portion (pars petrosa [pyramis]) (Fig. 48). The petrous portion 

 is a pyramidal process of bone wedged in at the base of the skull between the 

 sphenoid and occipital bones. Its direction from without is inward, forward, 

 and a little downward. It presents for examination an apex, four surfaces, and 

 three borders, and contains in its interior the essential parts of the organ of 

 hearing. 



Apex (apex pyramidis). The apex of the petrous portion, rough and uneven, 

 is received into the angular interval between the posterior border of the greater 

 wing of the sphenoid and the basilar process of the occipital; it presents the anterior 

 or internal orifice of the carotid canal (foramen caroticum interuum), and forms 

 the posterior and external boundary of the foramen lacerum medium. 



PROCESSUS 

 COCHLEARIFORMIS 



AQUEDUCT OF/ 



FALLOPIUS 



PROBE IN 

 TYMPANIC 

 CANAL 



SEMICANAL FOR 

 TENSOR TYMPANI 



PROBE IN 

 TYMPANIC CANAL 



Fir,. 50. Right temporal bone cut open. Lateral view of medial half of bone. X 2. (Spalteholz.) 



Surfaces. The superior surface of the petrous portion (Fig. 48) forms the 

 posterior part of the middle fossa of the skull; it looks upward and forward. 

 This surface is continuous with the squamous portion, to which it is united by 

 a suture, the petrosquamous suture, the remains of which are distinct- even at a 

 late period of life. 



The superior surface presents six points for examination: (1) An eminence 

 (eminentia arcuata) near the centre, which indicates the situation of the superior 

 semicircular canal. (2) In front and a little to the outer side of this eminence a 

 depression indicating the position of the tympanum; here the layer of bone which 

 separates the tympanum from the cranial cavity is extremely thin, and is known 

 as the tegmen tympani. The thin inferior extremity of this plate drops downward 

 and presents itself at the inner extremity of the Glaserian fissure, there making 

 the fissure double; the anterior slit is called the canal of Huguier, and it transmits 

 the chorda tympani nerve. (3) A shallow groove, sometimes double, leading 

 outward and backward to an oblique opening, the hiatus Fallopii (hiatus canalis 

 facialis), for the passage of the greater petrosal nerve and the petrosal branch of 



