SPECIAL ANATOMY OF THE SKELETON 



with the condyle of the mandible. The posterior part of the fossa lodges part of 

 the parotid gland, and is formed by the antero-inferior surface of the tympanic 

 portion. The fossa is crossed by an oblique fissure, the petrotympanic fissure 

 (Glaserian fissure}, which leads into the tympanum, lodges the processus gracilis 

 of the malleus, and transmits the tympanic branch of the internal maxillary 

 artery. This fissure is closed externally; at its inner extremity it is separated 

 from the squamous portion by the downgrowth of a process of bone from the 

 tegmen tympani (processus inferior tegmini tympani) of the petrous portion 

 between the squamous and tympanic plates, making the fissure at its internal 

 extremity a double one. The anterior limb is known as the canal of Huguier 

 (canaliculus chordae tympani}, and transmits the chorda tympani nerve. 



The external auditory meatus is bounded in front, below, and behind by the 

 tympanic portion. The roof and the upper part of the posterior wall are formed 

 by the squamous portion. The canal is about three-quarters of an inch (18 mm.) 

 in length, and is directed inward and forward. In vertical section it is of oval 

 outline, the long axis of the oval being vertical in the outer segment and oblique 

 in the inner segment. 



' The styloid process is a sharp spine of varying length. It projects downward 

 and forward from the vaginal process of the tympanic part, and gives origin 

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

 pharyngeus, and Stylohyoid muscles. 



Structure. The squamous portion is like that of the other cranial bones; the mastoid portion, 

 cellular; and the petrous portion, dense and hard. 



Development (Fig. 53). The temporal bone is developed from ten centres, exclusive of those 

 for the internal ear and the ossicles viz., one for the squamous portion, including the zygoma, 



one for the tympanic plate, six for the petrous 

 and mastoid parts, and two for the styloid 

 process. Just before the close of fetal life 

 the temporal bone consists of four parts: 

 1 for 

 squamous 

 portion, 

 including 



zygoma : 

 2d month. 



1 for tympanic 

 plate. 



6 for petrous 



and mastoid 



portions. 



2 for styloid process. 



(1) The squamozygomatic part, ossified in 

 membrane from a single nucleus, which 

 appears at its lower part about the second 

 month. (2) The tympanic plate, an imper- 

 fect ring, in the concavity of which is a 

 groove, the sulcus tympanicus, for the at- 

 tachment of the circumference of the tym- 

 panic membrane. This is also ossified from 

 a single centre, which appears in membrane 

 about the third month. (3) The petromas- 

 toid part, which is developed from six centres, 

 appearing in the cartilaginous car capsule 

 about the fifth or sixth month. Four of these 

 are for the petrous portion and are placed 

 around the labyrinth, and two are for the 

 mastoid (Vrolik). According to Huxley, the 

 centres are more numerous and are disposed 

 so as to form three portions: The first por- 

 tion includes most of the labyrinth (part of 



FIG. 53. Development of the temporal bone, 

 centres. 



From ten the cocn l ea . vestibule, superior semicircular 

 canals, and the inner wall of the tympanic 

 cavity) and a part of the petrous and mastoid. 



This portion he has named the pro-otic. The second portion the opisthotic consists of the rest 

 of the petrous, and is thus made up: the floor of the tympanum and vestibule surrounds the caro- 

 tid canal and the outer and lower portions of the cochlea and spread inward below the internal 

 auditory meatus. The third portion the pteriotic roofs the antrum and tympanic cavity. 

 The fourth portion the epiotic includes the remainder of the mastoid. The petromastoid 

 is ossified in cartilage. (4) The styloid process is also ossified in cartilage from two centres 

 one for the base, which appears before birth, and is termed the tympanohyal; the other, comprising 

 the rest of the process, is named the stylohyal, and does not appear until after birth. Shortly 

 before birth the tympanic plate unites with the squamous. The petrous and mastoid unite with 



