175 



which, in some of the mammalia, descends behind the condyle of the jaw. and 

 prevents it being displaced backward during mastication (Humphry). The poste- 

 rior part of the glenoid fossa, which lodges a portion of the parotid gland, is 

 formed chiefly by the tympanic plate, a lamina of bone, which forms the anterior 

 wall of the tympanum and external auditory meatus. This plate of bone termi- 

 nates externally in the auditory process, above in the Glaserian fissure, and below 

 forms a sharp edge, the vaginal process, which gives origin to some of the fibres of 

 the Tensor palati muscle. The Glaserian fissure, which leads into the tympanum, 

 lodges the processus gracilis of the malleus, and transmits the tympanic branch of 

 the internal maxillary artery. The chorda tympani nerve passes through a sepa- 

 rate canal, parallel to the Glaserian fissure (canal of Huguier), on the outer side of 

 the Eustachian tube, in the retiring angle between the squamous and petrous por- 

 tions of the temporal bone. 1 



The internal surface of the squamous portion (Fig. 139) is concave, presents 



parietal 



Aquseductus restibuli. 

 Depression for dura maier. 

 Meat its auditorius interims: 



Eminence for superior semicircular canal. 

 Hiatt'S Fallopii. 



Opening for smaller petrosal nercf. 

 Depi ession for Gasserian ganglion. 

 Bristle passed through carotid canal. 



FIG. 139. Left temporal bone. Inner surface. 



numerous eminences and depressions for the convolutions of the cerebrum, and 

 two well-marked grooves for the branches of the middle meningeal artery. 



Borders. The superior border is thin, bevelled at the expense of the internal 

 surface, so as to overlap the lower border of the parietal bone, forming the squam- 

 ous suture. The anterior inferior border is thick, serrated, and bevelled, alter- 

 nately at the expense of the inner and outer surfaces, for articulation with the 

 great wing of the sphenoid. 



The Mastoid Portion (aa<rr6c, a nipple or teat) is situated at the posterior part of 

 the bone : its outer surface is rough, and gives attachment to the Occipito-frontalis 

 and Retrahens aurem muscles. It is perforated by numerous foramina; one of 

 these, of lai-ge size, situated at the posterior border of the bone, is termed the 

 imixtoid foramen : it transmits a vein to the lateral sinus and a small artery from 

 the occipital to supply the dura mater. The position and size of this foramen 



1 This small fissure must not be confounded with the large canal which lies above the Eustachian 

 tube and transmits the Tensor tympani muscle. 



