CHAP, in.] SKELETON OF THE HEAD AND TRUNK. 



65 



In its natural state it is coated with cartilage, and serves for the 

 articulation of the lower jaw. This surface is limited behind by a 

 sharply descending bony plate the post-gknoid process (gp). A 

 ridge of bone is continued backwards from the hinder end of the 

 zygomatic process, over the external auditory meatus, and is called 

 the posterior root of the zygoma, the part supporting the glenoid 

 surface, forming the anterior root of the zygoma. 



The bone which bounds inferiorly the external auditory opening 

 is that which forms the auditory bulk already spoken of. This is 

 rounded, and smooth on the surface, and rather longer from before 

 backwards than transversely. It is at first made of two parts : an 

 external part, consisting of a crescentic plate of bone, broader 

 in front than behind the tympanic (so called on account of its 



Pig. 35. 



A. External view. 



B. Internal view. 



b. Inner and larger part of bulla. 



cb. Cerebellar fossa. 



cu. Eustachian opening. 



g. Glenoid surface. 



cip. Post-glenoid process. 



m. Mastoid region. 



me. Meatus auditorius externus. 



mi. Meatus auditorius internus. 



ms. Mastoid process. 



p. Surface applied to parietal. 



sq. Squamosal. 



t. Outer and smaller part of bulla. 



x. Aqueductus cochleae. 



z. Zygomatic process. 



12. Stylo-mastoid foramen. 



A process of the malleus is seen in Fig. A, ex- 

 tending downwards and forwards within the 

 auditory meatus. 





connexion with the drum of the ear) and an internal, much wider 

 part the ento-tympanic which forms all the rest of the bulla, 

 which is naturally visible on the base of the skull. 



Between the anterior end of the tympanic and the post-glenoid 

 process is a narrow chink, termed the fissura Glaseri, which transmits 

 the chorda tympani nerve. 



At the hinder end of the tympanic, beneath the posterior end of 

 the posterior root of the zygoma, is an opening (12), called the stylo- 

 mastoid foramen, which gives exit to the facial nerve. Immediately 

 below and within this foramen there is a small pit in the tympanic, 

 at the bottom of which a minute cylindrical ossicle, called the 

 tympano-hyal, may be detected, which serves to give attachment to 

 the uppermost and cartilaginous portion of the anterior, or lesser 

 cornu of the hyoid (Fig. 46, t*). 



The only remaining part of the temporal bone visible externally 

 is a very small and narrow triangular tract, which extends upwards 



