Part 3: Oral Cavity, Tongue, Pharynx, Larynx, and Associated Muscles

Turn the specimen over to the medial (cut) side to examine the mouth, or oral cavity. The mouth is divided into the vestibule and the oral cavity proper.

• Identify the superior and inferior (upper and lower) lips of your specimen.

• Identify the vestibule of the mouth. The vestibule is the cavity between the inside of the lips and cheeks and the outside of the teeth and gums. (The best illustration of this concept is to close your mouth tightly and then puff your mouth/cheeks up with air; the pockets of air are filling the vestibule.)

  • • Comment: Note that the parotid salivary duct and the duct of the zygomatic salivary gland both open into the dorsocaudal part of the vestibule.

• Identify the oral cavity proper, which is the cavity within the teeth and gums. The oral cavity proper is bounded dorsally by the hard palate (and part of the adjacent soft palate) and ventrally by the tongue and adjacent mucosa.

Inside the oral cavity, examine the palate dorsally. The palate is the partition between the oral cavity and the nasal cavity. Identify the hard palate, which is the bony rostral part of the palate, and the soft palate, which is the soft tissue extending caudally from the hard palate to the pharynx where it divides the nasopharynx from the oropharynx.

• Rostrally on the hard palate, look for the incisive papilla. This is a small eminence protruding from the roof of the mouth just caudal to the incisor teeth; note that this is a normal structure.

  • • Comment: On either side of the incisive papilla there is a fissure which represents the opening of the incisive duct.

Examine the tongue and note that it is divided into three regions: root, body & apex. Identify these regions on the tongue of your specimen.

• The root of the tongue is the caudal third of the tongue.

• The apex is the free extremity of the tongue at the rostral end.

• The body of the tongue is the long slender part of the tongue in between the root and the apex.

On the dorsal aspect of the tongue, note that the mucosa is modified to form various types of papillae. (See DG Fig. 5-23) The following five types of papillae are found on the tongue:

• filiform: The filiform papillae are the most numerous and cover most of the apex and body of the tongue. They are arranged in rows, and are elongated and cylindrical in shape, with their tips pointed caudally.

  • • Dissection Note: In the cat, the filiform papillae are fairly large and stiff and serve as an aid in grooming.

• conical: The conical papillae replace the filiform papillae at the root of the tongue. The conical papillae are cone-shaped, each with a singular tip pointing caudally.

• fungiform: The fungiform papillae have a smooth, rounded surface, like the top of a button mushroom, and are fewer in number than the filiform and conical papillae. They are found interspersed among the filiform papillae on the apex and body of the tongue. (Note that you may see a few scattered among the conical papillae at the root of the tongue as well.)

• foliate: The foliate papillae will be readily apparent in the CAT specimens, found on the lateral margins of the root of the tongue. They are leaf-like in appearance, especially in the cat, but in the preserved dogs, they often look more like a row of parallel grooves along the lateral sides of the root of the tongue.

• vallate: The vallate papillae are located at the junction of the body and root of the tongue. Typically, you will see 4-6 of them arranged in a V-shape configuration, with the apex of the V pointed caudally. The vallate papillae are the largest of the five papillae and have a raised inner circle surrounded by a sulcus (or a ‘moat’ as some call it).

• Comment: Note that there are taste buds found on the vallate, foliate and fungiform papillae.

Examine the ventral aspect (underside) of the tongue. Identify the ventral median fold of mucosa attaching the tongue to the floor of the oral cavity. This is the lingual frenulum. (See DG Fig. 5-24)

Turn the tongue medially and look for the sublingual caruncle that lies just lateral to the rostral part of the frenulum. This caruncle is a slightly raised ‘bump’ of mucosa that protrudes from the floor of the oral cavity.

• Extending caudally from the sublingual caruncle, identify the sublingual fold. This is a fold of mucosa which covers the salivary ducts of the mandibular and major sublingual salivary glands. These ducts run from each respective gland rostrally to empty on (or near) the sublingual caruncle into the oral cavity proper. (See DG Fig. 5-24)

  • • Incise the mucosa of the sublingual fold extending caudally from the sublingual caruncle. Bluntly dissect just deep to the mucosa to identify the salivary ducts.

In the CAT specimens only, identify the lingual molar salivary gland (previously referred to as the buccal salivary gland or buccal (molar) salivary gland).

• The lingual molar salivary gland is an additional salivary gland that cats have. It is located inside the oral cavity at the caudal aspect of each lower dental arch, up against the caudal aspect of the lower molar teeth.

  Related Learning Objective

  • D7.3

   

On the cut edge of each half of your head specimen, examine the region of the pharynx. The pharynx is the passage that is common (in part) to both the respiratory and digestive systems. It is located between the oral cavity proper and the esophagus. The pharynx is divided into three parts which you should identify: oropharynx, nasopharynx, and laryngopharynx. (See DG Fig. 5-25A & B)

• The oropharynx begins at the caudal portion of the oral cavity, between the soft palate dorsally and the root of the tongue ventrally. It extends to the base of the epiglottis, which marks the entrance to the larynx. Identify the oropharynx on each half of your split head.

  • • In the oropharynx, identify the palatoglossal arch (aka palatoglossal fold), which is the fold of mucosa extending vertically from the soft palate to the tongue on both left and right sides.

    • Caudal to the palatoglossal arch, within the lateral wall of the oropharynx on each half of the head, identify the palatine tonsil and the semilunar fold. Note that the semilunar fold partially covers the palatine tonsil. (See DG Figs. 5-24 and 5-26)

• The nasopharynx extends from the caudal portion of the nasal cavity to the caudal border of the soft palate. Identify the nasopharynx on each half of your split head.

  • In the nasopharynx, identify the palatopharyngeal arch (aka palatopharyngeal fold), which is the fold of mucosa extending caudally (horizontally) from the end of the soft palate.

  • On the lateral wall of the nasopharynx, locate the slit-like opening that is the opening to the auditory tube.

• The laryngopharynx is located dorsal to the larynx and rostral to the beginning of the esophagus. Identify the laryngopharynx on each half of your split head.

  • In the laryngopharynx, identify the pharyngoesophageal limen which serves as the border/transition between the pharynx and esophagus. (See DG Fig. 5-25A & B)

  • Identify the larynx, trachea and the tracheal cartilages (aka ‘tracheal rings’).

• Comment: Note that there are several pharyngeal muscles surrounding the pharynx externally; these include the cricopharyngeus m., thyropharyngeus m., and hyopharyngeus m. but you need not dissect or identify them. 

Examine the larynx from the medial (cut) side of each half of your specimen head. Determine which side has the ‘better’ larynx/most intact larynx and use that side of the head to proceed with your dissection.

Identify the cartilages that make up the larynx. These are the epiglottic, thyroid, cricoid, and arytenoid cartilages. (See DG Figs. 5-25A, 5-27, 5-28, 5-29, and 5-30)

• The epiglottic cartilage (aka epiglottis) marks the entrance to the larynx. Cranially, the epiglottic cartilage has a somewhat rounded free edge. Caudally it is attached to the thyroid cartilage. (See DG Figs. 5-23, 5-25A, 5-27, 5-28, 5-29, and 5-30)

• The thyroid cartilage forms a deep U (or ‘boat’) shape that is open on the dorsal side. It ‘cups’ the rest of the larynx and forms the lateral most walls. (See DG Figs. 5-25A, 5-27, 5-28, and 5-30)

  • • In order to better visualize the thyroid cartilage, make a small incision in the lateral wall of the mucosa adjacent to the larynx and reflect the mucosa away.

    • Note that on the ventral aspect, along the midline, the thyroid cartilage is notched by the caudal thyroid incisure, where the cricothyroid ligament attaches.

• The arytenoid cartilage is the only paired cartilage, with one on both left and right halves of the larynx. The arytenoids are irregularly shaped, but are said to resemble a butterfly, with 2 ‘wings’. The arytenoid cartilage is attached via mucosa to the epiglottis (the aryepiglottic fold) and articulates caudally with the cricoid cartilage. (See DG Figs. 5-27, 5-28, 5-29, and 5-30)

  • • The caudoventral process of the arytenoid cartilage is called the vocal process and is where the vocal fold (dog)/vocal ridge (cat) attaches the arytenoid to the thyroid cartilage. (See DG Figs. 5-25, 5-27, and 5-28)

    • In DOG specimens only, identify the laryngeal ventricle (dog only; absent in cat). The laryngeal ventricle is the diverticulum of the laryngeal mucosa craniomedial to the vocal fold. (See DG Fig. 5-28B)

• The cricoid cartilage forms a complete ring. It has a wide dorsal aspect and a narrow ventral aspect. (It resembles a class ring, being wide on the top of the finger, but a small band on the bottom side of the finger.) (See DG Figs. 5-25A, 5-27, 5-28, 5-29, and 5-30)

  • • As previously mentioned, there is a cricothyroid ligament connecting the cricoid cartilage to the thyroid cartilage. Attempt to identify this ligament on your specimen. If it is not visible, be sure to view it on a demonstration specimen.

Observe/understand the concept of the glottis. The glottis is the part of the larynx made up of the two vocal processes, the two vocal folds (or ridges), and the opening/narrow passageway between them.

Reflect the mucosa from the dorsal aspect of the larynx to identify the cricoarytenoideus dorsalis m. This muscle is found dorsally on the larynx, extending from the cricoid cartilage to the arytenoid cartilage. It’s primary function is to open the glottis. (See DG Figs. 5-28 and 5-30)

• Comment: Note there is also a cricoarytenoideus lateralis m. arising from the lateral aspect of the cricoid cartilage and inserting on the arytenoid cartilage. This muscles acts to close the glottis, but you need not dissect it on your specimens.

On the ventral aspect of the larynx, identify the cricothyroid m. (aka cricothyroideus m.) This muscle extends from the cricoid cartilage to the thyroid cartilage.

• Dissection Note: The two sides of the cricothyroid muscle create a ‘bowtie shape’ on the ventral aspect of the larynx.

  Related Learning Objective

  • D7.5

   

On the lateral side of the specimen, identify the digastricus m. found along the mandible. The digastricus is a muscle of mastication with two parts. The digastricus m. is involved with the action of opening the jaw. (See DG Figs. 2-12, 5-24, and 5-26)

• Transect the digastricus muscle through its approximate middle and reflect both parts.

Identify the mylohyoideus m. which is a thin ‘sling’ of muscle that spans the intermandibular space and helps support the tongue. (See DG Figs. 5-24, 5-25, 5-26A & B, 5-33, and 5-34)

• Carefully separate the thin layer of mylohyoideus m. and reflect it laterally and dorsally to see deeper muscles/structures on your specimen.

  Related Learning Objective

  • D7.6

   

After reflecting the mylohyoideus muscle, identify the styloglossus m. which lies deep to the digastricus m. The styloglossus m. arises from the stylohyoid bone and inserts in the middle of the tongue. It’s action is to retract and elevate the tongue. (See DG Fig. 5-33)

Medial to the styloglossus m., identify the hyoglossus m. extending from the hyoid apparatus to the root of the tongue. It acts to retract and depress the tongue. (See DG Fig. 5-33)

From the medial side of your specimen, identify the genioglossus m. extending from the chin (‘genio’) to the tongue (‘glossus’). The genioglossus lies partly in the lingual frenulum and acts to protrude the tongue and also to retract the apex of the tongue. (See DG Figs. 5-24, 5-25A, and 5-33)

While still on the medial side, identify the geniohyoideus m. extending from the chin (‘genio’) to the hyoid apparatus (‘hyoideus’). This muscle acts to draw the hyoid apparatus and larynx rostrally. (See DG Figs. 5-25A and 5-33)

Comment: Note there is also a thyrohyoideus m. extending from the thyroid cartilage to the hyoid apparatus, but you need not identify it. You may also see stumps of the sternohyoideus and sternothyroideus muscles, attaching to the hyoid apparatus and thyroid cartilage respectively. These were previously dissected and identified in Chapter 3.