Prelab Images - Ear & Nasal Cavity

Prelab should consist of reading the lab manual and dissector answers and viewing the dissection video. To begin your study, you may find it useful to look over the Netter's or LWW Atlas images listed below.

Step 1. Review the osteology of the temporal bone and nasal cavity. (Play movie)

Plate N92 or TG7-68 identifies the tegmen tympani. Plate N9 or TG7-70 shows the arcuate eminence and plate N92 or TG7-67 shows the anterior semicircular canal bulging into the arcuate eminence. External acoustic meatus (N8 or TG7-06), internal acoustic meatus (N11 or TG7-07), and the bony auditory tube (N67 or TG7-67, N92 or TG7-68A and TG7-68B) are all labeled. Plates N92 and N94 or TG7-68 show the tensor tympani traveling within a semicanal in the bone that forms the auditory tube. Hiatus for the greater and lesser petrosal nerves are labeled in plate 11 or TG7-07. The petrotympanic fissure and (inferior) tympanic canaliculus are labeled in plate N8 or TG7-06. Plates N92 or TG7-68 and N94 or TG7-70 show the promontory, vestibular (oval) window, cochlear (round) window, opening of the auditory tube, and prominence of the facial canal. Plate N4 or TG7-04 shows the close proximity of the external acoustic meatus to the mandibular fossa. Plate N92 or TG7-65 shows the outer, middle, and inner ear. These three parts of the ear are briefly described in the lab manual. Plates N92 or TG7-65 and N94 or TG7-68 show the middle ear or tympanum and its contents. Plates N55, N65 or TG7-24, N67 or TG7-22, N92 or TG7-65, and N94 or TG7-68 all give different views of the auditory (Eustachian) tube, which runs from the ear to the nasopharynx (N63 or TG7-23, N64). Plate N4 or TG7-32 labels the pterygopalatine fossa and sphenopalatine foramen. Plate N2 or TG7-03 shows the nasal aperture (opening) and labels the nasal bone. Plates N8 or TG7-06 and N65 or TG7-21 label the pharyngeal tubercle. The medial pterygoid plate and the pterygoid hamulus are illustrated in plates N6 or TG7-08 and N8 or TG7-06. The maxilla is identified in plate N2 or TG7-03. The vomer and perpendicular plate of the ethmoid bone are shown in plate N6 or TG7-08. Plates N6 or TG7-08, N48 or TG7-41, and N49 or TG7-44 identify the sphenoid, frontal, and maxillary sinuses. Superior, middle, and inferior nasal conchae are shown in plate N6 or TG7-08. Plate N49 or TG7-44 labels ethmoidal air cells. Plate N63 or TG7-06 shows the hard palate.

Step 2. On the decalcified temporal bone, identify the structures of the anterolateral surface of the middle ear cavity. (Play movie)

Each lab group will receive a temporal bone that has been soaked in acid to decalcify the bone (making it easy to dissect the bone with a scalpel). Plate N86 or TG7-67 shows the greater petrosal nerve passing under the trigeminal ganglion on its way to the foramen lacerum (N11 or TG7-07). Remove the dura mater and reflect the trigeminal ganglion to trace the greater petrosal nerve. Plate N86 or TG7-67 also shows the lesser petrosal nerve passing just lateral to the greater petrosal nerve. The lesser petrosal nerve originates from the tympanic plexus (plate N94 or TG7-68) that is formed on the promontory (N94 or TG7-68) by the tympanic branch of the glossopharyngeal nerve. Plates N123 or TG7-84 and N125 or TG7-90 show the lesser petrosal nerve going to the otic ganglion. Next, snip away the squamous part of the temporal bone (N9 or TG7-07) so the posterior floor of the middle cranial fossa is accessible. Remove the roof of the external acoustic meatus as far medially as the tympanic membrane (N92 or TG7-65). Shave through the tegmen tympani (N92 or TG7-65) to reveal the epitympanic recess (N92 or TG7-65 and N93) below. Plates N92 or TG7-65, N93, and N94 or TG7-68 show the malleus and the incus and the parts of these bones are shown in plate N93. Plate N94 or TG7-68 labels the mastoid antrum. A small opening connects the epitympanic recess to the mastoid antrum posteriorly. This path is called the aditus ad antrum and can be seen in plate N94 (unlabeled) or TG7-68A (it is the area with the superior ligaments of the incus and malleus passing through it). Plates N92 or TG7-68A and N94 or TG7-68B show the facial nerve and the facial canal. Plate N97 or TG7-67 shows the geniculum (bend) of the facial nerve. The geniculate ganglion is located at this geniculum. The greater petrosal nerve also branches off the facial nerve at the geniculate ganglion. See plate N123 or TG7-87 for the facial nerve. Cut through the greater petrosal nerve (N86 or TG7-67) near the foramen lacerum (N10 or TG7-07) and reflect it back to expose the bone covering the tensor tympani muscle. Plate N94 or TG7-68 shows that if you shave through the bone just below the greater petrosal nerve you will reach the tensor tympani muscle. The muscle is separated by a thin bony septum from the auditory tube below (N94 or TG7-68).

Step 3. Identify the structures of the posteromedial wall of the middle ear cavity. Review the nerves related to the temporal bone and middle ear. (Play movie)

Plates N8 or TG7-06, N9 or TG7-07, and N11 or TG7-08 identify the external auditory meatus, petrous ridge, and internal auditory meatus. Plate N104 or TG7-51 shows cranial nerves VII and VIII entering the internal acoustic meatus. Plate N9 or TG7-07 shows the arcuate eminence, which you can shave through to find the anterior semicircular canal (N92 or TG7-65). If you shave through the bone anterolateral to the arcuate eminence you will enter the epitympanic recess (N92 or TG7-65) and see the malleus articulating with the incus. Plate N93 or TG7-69 identifies the short and long limb or process of the incus and plates N92 or TG7-65 and N93 or TG7-68 show how the incus articulates with the head of the stapes. Plates N94 and N92 or TG7-65 show the auditory tube and the inverted "J" shape of the cartilage is seen in plate N92 or TG7-67. The tympanic membrane, auditory tube, incus, malleus, tensor tympani muscle, chorda tympani, mastoid antrum, and air cells can all be seen in plate N94 or TG7-65. Plates N92 or TG7-65 and N93 show the long process of the incus articulate with the stapes. The chorda tympani can be seen in plates N93 and N94 or TG7-68 passing between the malleus and the incus. It is a branch of the facial nerve (N123 or TG7-87). Plate N8 or TG7-06 shows the petrotympanic fissure and plate N93 or TG7-68 shows the tendon of the tensor tympani muscle. Plates N92 or TG7-65, N93 or TG7-66, and N94 or TG7-68 all show the malleus attaching to the tympanic membrane. Plate N93 or TG7-68 shows the base (footplate) of the stapes, which lodges into the oval (vestibular) window in plates N92 or TG7-70 and N94 or TG7-69. The promontory, stapes, oval window, round window, and canal for the facial nerve are shown in plates N92 or TG7-68 and N94 or TG7-70. The tendon of the stapedius muscle is shown in plates N93 or TG7-68 and N94 or TG7-69. Next, shave off the bone covering the internal acoustic meatus to identify the facial and vestibulocochlear nerves, cochlea, and the semicircular canals (see plate 97 or TG7-67). The vestibule of the internal ear is identified in plates N92 or TG7-70 and N96. Plate N103 or TG7-67 shows the geniculum of the facial nerve where the geniculate ganglion is located. The greater petrosal nerve will emerge near the geniculum and travel in the groove for the greater petrosal nerve (plate N102 or TG7-07). Also, see plate N82 or TG7-60 for the course of the greater petrosal nerve. Plate N123 or TG7-87 reviews the facial nerve. Plates N11 or TG7-65, N94 or TG7-68A, N93 or TG7-67, N95 or TG7-68B, N86, N123, N131, and N136 all give views that show how close the structures of the ear are to the carotid canal.

Step 4. Examine the nasal cavity, its regions and internal structures. (Play movie)

Plate N43 or TG7-41B shows the nasal cavity and the nasal septum. Plate N40 or TG7-41A shows the cartilaginous and bony parts of the nose. Plates N46, N47 or TG7-43, and N125 or TG7-45 or TG7-77 feature the olfactory nerve (CN I). You can find the tiny olfactory nerves by dissecting just inferior to the cribriform plate of the ethmoid bone. Plate N1 or TG7-03 identifies the nares. The vestibule and conchae (superior, middle, and inferior) are identified in plate N41 or TG7-43. This plate also identifies the superior, middle, and inferior meatuses and the sphenoethmoidal recess.

Step 5. Remove the conchae on one side to expose the meatuses, the ethmoidal bulla and hiatus semilunaris and the openings of the sinuses. (Play movie)

Plate N41 or TG7-43 shows the middle and inferior conchae cut away like you will need to do during lab. Plates N41 or TG7-43 and N42 show the opening of the nasolacrimal duct in the inferior meatus. The middle meatus has the semilunar hiatus (with the openings of anterior ethmoidal air cells), ethmoidal bulla (with the openings of middle ethmoidal air cells), the frontonasal duct (leading to the frontal sinus), and the opening of the maxillary sinus. See plate N41 or TG7-43 for the structures that open into the middle meatus. Plates N41 or TG7-43 and N42 or TG7-44 show the superior meatus, which contains the openings of the posterior ethmoidal air cells and the opening to the sphenoid sinus. Plate N41 or TG7-43 shows the hypophysis very near to the sphenoid sinus. The internal carotid artery is shown passing just beside the sphenoid sinus in plate N106 or TG7-72. Plates N52 and N53 or TG7-43 explore the extent of the maxillary sinus and ethmoidal air cells. Review the drainage the sinuses and air cells into the nasal cavity (N41 or TG7-44).

Plate N73 or TG7-19 shows the external carotid artery giving off the maxillary artery. Plates N44 or TG7-35 and N45 or TG7-45 show this artery giving off the sphenopalatine artery, which passes through the sphenopalatine foramen to supply the nasal cavity. The anterior and posterior ethmoidal arteries also supply the nasal cavity and are labeled in plate N45 or TG7-45 as well. Plates 46 and 47 or TG7-45 show the olfactory nerve passing through the cribriform plate of the ethmoid.

Step 6. Examine the muscles of the soft palate associated with the auditory tube. (Play movie)

Plates N63 or TG7-23 and N64 or TG7-24 show the soft palate, uvula, and the hard palate. The hamulus of the medial pterygoid plate can be seen in the oral cavity in plate N52 or TG7-06. The opening of the auditory tube into the nasopharynx is labeled in plates N37 or TG7-23 and N64. The torus tubarius is shown encircling the opening of the auditory tube in plate N37 or TG7-23. The pharyngeal recess in labeled in plates N37 or TG7-23 and N64 just posterior to the torus tubarius. The pharyngeal tonsil is also labeled in plates N37 or TG7-23 and N64. Plates N68 or TG7-23, N69 or TG7-24, and N68 or TG7-22 or TG7-67 show the levator veli palatini muscle and the tensor veli palatini muscle. Expose the insertion of the tensor veli palatini muscle by removing the mucous membrane from the inferior surface of the soft palate. Plate N64 or TG7-23 identifies the palatoglossal and palatopharyngeal folds (arches). The tonsillar fossa is shown in plates N63 or TG7-39 and N64 (unlabeled). This fossa contains the palatine tonsil (N63 or TG7-39 and N64). Plate N64 or TG7-24 shows the superior pharyngeal constrictor muscle deep to the palatine tonsil. Plates N63 or TG7-39 and N64 identify the lingual tonsil at the root of the tongue posterior to the foramen cecum.