making a right or obtuse angle with the outer surface of the mastoid process. In the latter case the sigmoid groove often approaches close to the posterior bony wall (Plate 6, Trautmann). Immediately in front of the drumhead the bony floor of the auditory canal is convex above and forms an acute angle (27 degrees) with the membrane. This space, known as the recessus meatus acusticus externus (Plate 3), often becomes a lodging-place for small foreign bodies. The floor of the canal is longer than the roof, and accordingly extends further into the interior. The anterior wall is longer than the posterior, and, like the floor, extends farther in than the posterior wall.

The lumen is greater at the two extremities than at the middle of the canal; in the cartilaginous portion it contracts uniformly from without inward. In the bony portion the contraction is greatest at the inner third (isthmus), where foreign bodies are apt to be found (see Fig. 3). The length of the auditory meatus is about 14 mm.; that of the cartilaginous portion, measured from the tragus, 21 mm., the entire length being, therefore, about 35 mm. (Bezold) (Plate 4).

Histology (Plate 13).-The skin covering the cartilaginocutaneous portion of the canal presents small papill below the epidermis, and a number of hairs with tubular sebaceous glands and about 1500 large ceruminous glands, the latter consisting of cuboid epithelial cells containing a brownish granular pigment imbedded in the subcutaneous stratum. The narrow ducts of these glands, after making a sharp bend, terminate in a common depression with hair-follicles and sebaceous glands. The pigmented secretion from these glands, mingling with the fat from the sebaceous glands and desquamated epithelium, forms cerumen which often contains pathogenic micro-organisms (Rohrer) and the demodex folliculorum. The skin covering the bony meatus is thin except in that portion (the posterior portion of the roof) which is derived from the superficies meatus, where it is thicker

and also contains hairs and glands; this wedge-shaped strip of skin extends down as far as the drumhead (Plate 31).

(Petrous Portion (Plates 1, 2, 5).-The petrous portion of the pyramid in the new-born is distinguished from that of the adult by its size and the greater distinctness of the bony ridges. The petrous portion presents a quadrilateral pyramid. The anterior border, assisted by the sphenoid bone, forms the foramen lacerum anterius (Plate 11), which transmits the carotid artery, Eustachian tube, and the great and lesser superficial petrosal nerves. The upper border presents a groove that lodges the superficial petrosal sinus; the posterior border lodges the inferior petrosal sinus, and forms, with the occipital bone, the foramen lacerum posterius, or jugular foramen. The latter is divided by a bony spine into a smaller anterior compartment for the transmission of the glossopharyngeal, vagus, and spinal accessory nerves, and a larger posterior compartment for the transmission of the internal jugular vein (Plate 5). The lower border forms a sharp ridge on the continuation of the mass of bone that surrounds the styloid process. The anterior upper surface of the pyramid presents at its apex a depression that lodges the semilunar ganglion of the fifth nerve, and on the outer side of the depression two parallel grooves with separate openings: a median opening that transmits the great superficial petrosal nerve to the spurious opening in the Fallopian canal (a bristle introduced into the stylomastoid foramen emerges at this opening), and a lateral opening that transmits the small superficial petrosal nerve to the apertura superior canaliculi tympanici (Plate 5). About the middle of the pyramid, near its upper border, there is a bony ridge (eminentia arcuata) that overlies the superior semicircular canal (Plates 2, 7, 8). When, as occasionally happens, there is a defect in this ridge, pus may pass through the labyrinth to the brain. To the outer side of this ridge is a smooth plate of bone about the thickness of paper, and occasion

ally, especially in brachycephalic subjects, divided by a fissure that contains pneumatic cells. It is the tegmen tympani et antri (roof of the tympanum and antrum), and permits the passage of pus from the middle ear to the middle fossa of the skull. It is joined to the squamous portion of the tegmen by the petrosquamous suture.

The roof of the tympanum and antrum supports the third temporal convolution, to the inner side of which is found the fusiform gyrus of the occipital lobe, while still farther inward, on the apex of the pyramid, is found the hippocampal gyrus, a continuation of the lingual convolution of the occipital lobe (Plate 10). About the middle of the posterior superior surface of the pyramid there is an oval opening, the porus acusticus internus, which transmits the auditory and facial nerves, and the internal auditory artery and vein (Plates 2, 13, 4, 5). The floor of the internal auditory meatus is divided by a transverse ridge, the falciform crest, into an upper and a lower fossa (see Fig. 14). The upper fossa presents, in front, near the apex of the pyramid, an opening for the seventh nerve, and behind this several canaliculi forming the superior cribriform area (area cribrosa superior sive vestibularis), which transmits the utricular and the superior and lateral ampullary nerves. The lower fossa in front presents a number of spiral openings (tractus spiralis foraminosus) with a large central foramen (foramen centrale) for the passage of the cochlear portion of the auditory nerve, and behind this another foramen (the foramen singulare) for the transmission of the inferior ampullary nerve. Between and above these two foramina are several smaller openings constituting the middle cribriform area (area cribrosa media sive vestibularis inferior) for the saccular nerve. These foramina may become channels for the passage of pus from the labyrinth to the posterior fossa of the skull. On the posterior surface of the pyramid, especially in the new-born, the superior and posterior horizontal canals appear very distinetly (Plate 2). Underneath there is a cleft in the

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bone that communicates with the external opening of the aquæductus vestibuli. This also affords passage for pus from the labyrinth to the posterior fossa of the skull (Plates 2, 7). The superior semicircular canal is undermined by a fossa that contains vascular connective tissue (fossa subarcuata), and allows pus to pass from the interior of the petrous portion to the posterior fossa of the skull. Behind the porus acusticus internus the great horizontal fissure of the cerebellum comes in relation with the trous portion; while in front of the porus acusticus internus, between the petrous portion and the middle peduncle of the cerebellum, there is a lateral diverticulum of the subarachnoid space (Zuckerkandl) (Plate 10). On the posterior inferior surface of the pyramid, between the mastoid process and the styloid process, the stylomastoid foramen transmits the seventh nerve and the stylomastoid artery and vein. In front lies the jugular fossa, which is usually deeper on the right than on the left side, and lodges the bulb of the jugular vein (Plate 5); this is sometimes defective and permits pus to pass from the tympanic cavity to the bulb (Plate 17). A small foramen within the fossa transmits the auricular nerve (a branch of the vagus) to the tympanomastoid fissure.

Behind the anterior portion of the postero-inferior surface of the pyramid, which unites with the occiput by means of the petrobasilar suture (Plate 11), is the external opening of the carotid canal, which transmits the internal carotid artery, with its accompanying plexus of veins and the sympathetic nerve plexuses. The walls of the canal are pierced by small foramina (canaliculi caroticotympanici) through which small blood-vessels enter the tympanic cavity. These may form pus-channels from the tympanic cavity to the carotid (Plate 5). Between the jugular fossa and the external opening of the carotid canal is a small depression, the fossula petrosa, for the reception of the petrosal ganglion of the ninth nerve. Through a foramen in this fossa (apertura externa canaliculi tympanici) the tympanic nerve passes into the

tympanic cavity (Plate 5). Behind and to the median side of the latter is an infundibuliform depression (Plates 7, 8) leading into the aqueduct of the cochlea (apertura externa aquæductus cochleæ). Through this channel pus may pass from the labyrinth into the subarachnoid space of the posterior fossa of the skull. On the anteroinferior surface of the pyramid the internal carotid emerges from the bone through the apertura interna canaliculi carotici. To its outer side and sometimes separated by a thin plate of bone (pus-channel from the Eustachian tube to the carotid artery) lies the canalis musculotubarius (Plates 1, 5). The latter is divided by a thin plate of bone into an upper compartment for the tensor tympani and a lower compartment for the Eustachian tube.

In the adult the posterior segment of the anteroinferior surface of the pyramid, which enters into the formation of the tympanic cavity, is covered by the anterior bony wall of the auditory meatus and by the drumhead; in the new-born it is freely exposed by removing the membrane (Plate 1). The median wall of the tympanic cavity and outer covering of the beginning of the cochlea is formed by the wall of the promontory. The latter consists of a plate of bone, convex externally, with two openings lodged in depressions or foveæ,-the fenestra vestibuli (ovalis) and the fenestra cochleæ (rotunda), the corresponding foveæ bearing the same. appellations (pus-channels from the tympanic cavity into the labyrinth-Plates 1, 5). The promontory is traversed by a groove running from below upward, which lodges the tympanic nerve and artery.

Above and in front of the fenestra vestibuli is an excavated plate of bone, the processus cochleariformis, for the attachment of the tendon of the tensor tympani muscle. It forms the posterior extremity of the upper segment of the canalis musculotubarius. The lower segment, corresponding to the bony portion of the Eustachian tube, begins at the tympanic opening of the tube in the