l82 



HUMAN ANATOMY. 



the origin of the levator palati and tensor tympani muscles. External to the back 

 of this is the round orifice of the carotid canal^ ; back of this, and more internal, is 

 \\\Q jugular fossa. This presents two extreme types, entirely different, with inter- 

 mediate forms. It may be a large thimble-shaped hollow, the edge of which bounds 

 the venous part of the jugular foramen internally, forming a large reservoir for the 

 blood of the lateral sinus as it leaves the skull. On the other hand, it may be a 

 small flat surface. A minute, but very constant, foramen in the ridge between it and 

 the carotid canal transmits the tympanic branch of the glosso-pharyngeal nerve. A 

 nViXiwV^ foramen, usually found in the jugular fossa, transmits the auricular branch of 

 the vagus. The aqucedudus cochlear ends at a small triangular opening^ in front of the 

 jugular fossa, close to the inner edge. Behind the fossa is a small surface where the 

 temporal bone is united to the occipital, first by cartilage and then by bone. The 

 stylo- mastoid foramen, the orifice of the facial canal for the facial nerve, is near 

 the outer edge of this surface. The stylo-mastoid branch of the posterior auricular 

 .artery enters it. 



Fig. 203. 



SQUAMOUS PORTION 



Zygoma 



Zygomatic tubercle 



Groove for meningeal artery 



Foramen for lesser superficial pe- 

 trosal ner\'e 

 Hiatus Fallopii 



Depression for Gasserian ganglion 

 Eustachian tube 



Carotid canal 

 APEX OF PETROUS 



Carotid canal (lower end) 



Tympanic plate 

 Vaginal process 



Styloid process 



Right temporal bone from before. 



The anterior surface of the petrous is nearly all hidden by the tympanic 

 plate. It forms the inner wall of the cavity of the tympanum and of the bony part of 

 the Eustachian tube, which leaves the bone in the entering angle between this surface 

 of the petrous and the tympanic. The features of this surface are treated in the 

 section on the ear. T\\q processus cochlear if ormis^ attached like a shelf to this outer 

 wall, divides the canal for the tensor tympani muscle from the Eustachian tube 

 below it. The front of this plate can be seen at the entering angle, where the bony 

 tube ends. The small portion of the outer surface of the petrous which is visible 

 is in front of this point, and rests against the inner edge of the great wing of the 

 sphenoid. 



The superior internal border of the petrous is a prominent ridge in the base 

 of the skull, separating the middle and the posterior fossae. The tentorium is 

 attached to it. The superior petrosal sinus runs along it in a shallow groove within 

 the attached border of the tentorium. Near the front a groove by which the fifth 

 nerve reaches the Gasserian ganglion crosses this border. 



The inferior internal border articulates anteriorly with the basilar process of 



^ Canalls caruticus.  Apertura externa aquavductas cochleae. ^Septum canalis musculotubaril. 



