8o A MANUAL OF ANATOMY 



mastoid process ; and twigs from the mastoid division of the 

 posterior auricular, through the foramina on the outer surface of 

 the mastoid portion. 



Articulations. — These are usually five in number, as follows : 

 posteriorly and internally with the occipital, superiorly with the 

 parietal, anteriorly with the sphenoid and malar, and externally 

 with the condyle of the inferior maxilla, the latter being a movable 

 articulation. Sometimes the temporal articulates with the frontal, 

 giving rise to a fronto-squamosal suture. 



Structure. — The squamous portion is thin, and is practically 

 composed of two plates of compact bone. The mastoid portion 

 is thick, and, as stated, contains the mastoid antrum and mastoid 

 cells. The petrous portion is remarkable for its hardness, and it 

 contains all the divisions of the organ of hearing, except the carti- 

 laginous pinna on the outer side of the head. Thus it contains 

 (i) the osseous external auditory meatus; (2) the tympanum or 

 middle ear, with its three ossicles, malleus, incus, and stapes, etc. ; 

 and (3) the osseous labyrinth or internal ear, which contains the 

 membranous labyrinth, consisting of the utricle, saccule, semicircular 

 canals, and membranous cochlea. It also contains, for a certain 

 distance, extensions of the mastoid cells. 



Varieties. — (i) Foramen of Huschke in the centre of the tympanic plate, due 

 to imperfect ossification. (2) Absence of petro-squamous suture. (3) Absence 

 of the foramen within the hiatus Fallopii for the external superficial petrosal 

 nerve. 



Ossification. — The temporal bone is developed in three parts, namely; 

 squamosal, tympanic, and petrosal. The squamosal and tympanic elements 

 are formed in membrane, and the petrosal in cartilage. The squamosal gives 

 rise to the squamo-zygomatic portion, and the upper and front part of the 

 mastoid portion ; the tympanic forms the tympanic annulus ; and from the 

 petrosal are developed the petrous portion and the greater part of the mastoid 

 portion. It is to be noted that the mastoid portion is not an independent 

 part developmentally, but belongs chiefly to the petrous and partly to the 

 squamosal portions. The centre for the squamosal appears towards the end 

 of the second month of intra-uterine life in the region of the root of the zygoma, 

 and from this ossification extends upwards into the squamosal, forwards into 

 the zygoma, and inwards into the glenoid fossa in front of the Glaserian 

 iiSsure. From the posterior part of the squamosal a downward growth of 

 bone takes place below the supramastoid crest, called the postauditory process, 

 which forms the outer wall of the mastoid antrum, and gives rise to the upper 

 and front part of the mastoid portion. The centre for the tympanic element 

 appears towards the end of the third month of intra-uterine life in the lower 

 part of the external membranous wall of the tympanum, and from this is 

 developed the tympanic annulus. This ring forms about five-sixths of a 

 circle, the deficiency being above, where it is closed by the squamosal, and 

 within the circumference of the ring there is a groove for the membrana 

 tympani. Previous to birth the extremities of the ring become ankylosed 

 to the squamosal, and the tympanic plate is formed by an outward growth 

 from it, so that it is ultimately located at the deep end of the external auditory 

 meatus. The petrosal element or periotic cartilaginous capsule is developed 

 from four centres, which appear towards the end of the fifth month, and from 

 which ossification proceeds rapidly, union between the four centres being 

 effected by the end of the sixth month of intra-uterine life. These centres 

 are called opisthotic, pro-otic, pterotic, and epiotic, in the order of their appear- 



