PLATE 17.

Fig. 1. Exostosis on the Squamous Portion of the Temporal Bone and Hyperostosis of the External Auditory Meatus (B.).-Right temporal bone seen from in front: 1, Exostosis on the squamous portion (added from another temporal bone); 2, leaf-shaped suprameatal spine; 3, constricted heart-shaped auditory meatus.

Fig. 2. Gaping Posterior Half of Median Wall of Tympanic Cavity and Bulla Jugularis (B.).-Left tympanic cavity seen from in front, after removing the anterior bony wall of the auditory meatus. The bulb of the jugular vein was closely applied to the tympanic membrane and covered by the mucous membrane of the tympanic cavity: 1, Promontory with fenestra vestibuli and cochleæ; 2, gap.

Fig. 3. Anterior Displacement of Genu Caroticum (B.).--The right tympanic cavity after removal of the anterior bony wall of the auditory meatus seen from in front. The carotid canal (1) reaches almost to the promontory (2) in the tympanic cavity.

Fig. 4. Downward Displacement of the Middle Fossa of the Skull and Forward Displacement of the Transverse Sinus (B.).-Right temporal bone; the osseous portion of the attic (1) removed after Stacke; the mastoid antrum opened through the auditory meatus; the lateral portion of the posterior bony wall of the auditory meatus has been left (2) in place. By opening the mastoid process (4 cm. behind the suprameatal spine (3)), the dura mater of the cerebrum (4) at a point cm. below the supramastoid crest (5) and the transverse sinus (6) were exposed; the lower extremity of the latter approaches within 4 mm. of the posterior bony wall of the auditory meatus; 7, promontory.