

THE TEMPORAL BONE 145 



jugular foramen ; an eminence occasionally projects from the center of the fossa, 

 and divides the foramen into two. The anterior angle is divided into two parts 

 a lateral joined to the squama by a suture (petrosquamous) , the remains of which 

 are more or less distinct; a medial, free, which articulates with the spinous process 

 of the sphenoid. 



At the angle of junction of the petrous part and the squama are two canals, 

 one above the other, and separated by a thin plate of bone, the septum canalis 

 musculotubarii (processus cochleariformis) ; both canals lead into the tympanic 

 cavity. The upper one (semicanalis m. tensoris tympani) transmits the Tensor 

 tympani, the lower one (semicanalis tuba* auditivce) forms the bony part of the 

 auditory tube. 



The tympanic cavity, auditory ossicles, and internal ear, are described with 

 the organ of hearing. 



Tympanic Part (pars tympanica). The tympanic part is a curved plate of bone 

 lying below the squama and in front of the mastoid process. 



Surfaces. Its postero-superior surface is concave, and forms the anterior wall, 

 the floor, and part of the posterior wall of the bony external acoustic meatus. 

 Medially, it presents a narrow furrow, the tympanic sulcus, for the attachment 

 of the tympanic membrane. Its antero-inferior surface is quadrilateral and slightly 

 concave; it constitutes the posterior boundary of the mandibular fossa, and is 

 in contact with the retromandibular part of the parotid gland. 



Borders. Its lateral border is free and rough, and gives attachment to the car- 

 tilaginous part of the external acoustic meatus. Internally, the tympanic part 

 is fused with the petrous portion, and appears in the retreating angle between 

 it and the squama, where it lies below and lateral to the orifice of the auditory 

 tube. Posteriorly, it blends with the squama and mastoid part, and forms the 

 anterior boundary of the tympanornastoid fissure. Its upper border fuses laterally 

 with the back of the postglenoid process, while medially it bounds the petro- 

 tympanic fissure. The medial part of the lower border is thin and sharp; its lateral 

 part splits to enclose the root of the styloid process, and is therefore named the 

 vaginal process. The central portion of the tympanic part is thin, and in a consid- 

 erable percentage of skulls is perforated by a hole, the foramen of Huschke. 



The external acoustic meatus is nearly 2 cm. long and is directed inward and 

 slightly forward: at the same time it forms a slight curve, so that the floor of the 



(canal is convex upward. In sagittal section it presents an oval or elliptical shape 

 with the long axis directed downward and slightly backward. Its anterior wall 

 and floor and the lower part of its posterior wall are formed by the tympanic 

 part; the roof and upper part of the posterior wall by the squama. Its inner 

 end is closed, in the recent state, by the tympanic membrane; the upper limit 

 of its outer orifice is formed by the posterior root of the zygomatic process, imme- 

 diately below w r hich there is sometimes seen a small spine, the suprameatal spine, 

 situated at the upper and posterior part of the orifice. 



Styloid Process (processus styloideus) . The styloid process is slender, pointed, 

 and of varying length; it projects downward and forward, from the under surface 

 of the temporal bone. Its proximal part (tympanohyal) is ensheathed by the 

 vaginal process of the tympanic portion, while its distal part (stylohyal) gives 

 attachment to the stylohyoid and stylomandibular ligaments, and to the Stylo- 

 glossus, Stylohyoideus, and Stylopharyngeus muscles. The stylohyoid ligament 

 extends from the apex of the process to the lesser cornu of the hyoid bone, and 

 in some instances is partially, in others completely, ossified. 



Structure. The structure of the squama is like that of the other cranial bones: the mastoid 

 portion is spongy, and the petrous portion dense and hard. 



Ossification. The temporal bone is ossified from eight centers, exclusive of those for the internal 

 ear and the tympanic ossicles, viz., one for the squama including the zygomatic process, one for 

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