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Lab Objectives:

• Examine the larynx:
      - wall cartilages (epiglottic, thyroid, and cricoid)
      - the glottis (vocal folds attached to vocal processes of arytenoid cartilages & glottal cleft)
      - intrinsic muscles that manipulate arytenoid cartilages

• Examine the external ear canal externally and internally.

• Identify muscles comprising the different muscle groups of the head:
      - mastication muscle group (one of the muscles opens the jaw)
      - tongue (three extrinsic muscles)
      - hyoid muscle group (attach to the hyoid apparatus)

• Find the zygomatic salivary gland, after removing the temporal muscle.

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Anatomical Terms:

        Larynx:
        epiglottic cartilage
                aryepiglottic fold
        thyroid cartilage
                rostral cornu & caudal cornu
                caudal thyroid incisure
        cricoid cartilage
                cricothyroid ligament
        arytenoid cartilage
                vocal process
                muscular, corniculate & cuneiform processes
        vestibular fold
        laryngeal ventricle (absent in the cat)
        glottis
                vocal fold (cat: vocal ridge)
                        vocal ligament
                        vocalis muscle
                rima glottidis (glottis cleft)
        Intrinsic muscles of larynx:
                cricothyroid m.
                cricoarytenoideus dorsalis m.
                cricoarytenoideus lateralis m.
                thyroarytenoideus m.
                        vocalis m.

        External Ear:
        auricle (pina)
                auricular cartilage
                marginal cutaneous sac
                helix, tragus, incisures, etc
        external ear canal
                annular cartilage

        Muscles of Mastication
        temporalis m. (temporal m.)
        masseter m.
        medial & lateral pterygoid mm.
        digastricus m.

        zygomatic salivary gland

        Lingual Muscles
        styloglossus m.
        hyoglossus m.
        genioglossus m.

        Hyoid Muscles
        sternohyoideus m.
        thyrohyoideus m.
        mylohyoideus m.
        geniohyoideus m.

        Note:
             glottis [Greek: glottis] = vocal apparatus of the larynx
             thyroid [Greek: thyreos = shield & eidos = form] resembling a shield
             cricoid [Greek: krikos = ring & eidos = form] resembling a ring
             arytenoid [Greek: arytaina = ladle & eidos = form] resembling a ladle (?)

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Instructor Commentary:

The glottis (bilateral vocal folds, each attached to the vocal process of a mobile arytenoid cartilage) is critical to the two major functions of the larynx: 1] to close the airway to the lungs and prevent the inhalation pneumonia that would result from inhaling bacterial laden ingesta; and 2] to vocalize as a means of communicating with others.

Intrinsic laryngeal muscles manipulate the glottis via attachment on arytenoid cartilage. Damage to the recurrent laryngeal nerve and paralysis of the cricoarytenoideus dorsalis m. results in an inability to abduct the vocal fold, leading to a narrowed airway and a noise (roaring) during running. This condition (which is more common in horses) and reduction of excessive barking are two reasons for surgically removing or altering vocal folds so they remain permanently abducted.

Purring in the cat involves increasing air pressure caudal to a closed glottis. When air pressure exceeds the closure pressure of the glottis, a burst of air escapes, temporarily lowering air pressure until it again builds to reach closure pressure. The process is repeated over and over again.

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Dissection Images:

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