Suspensory apparatus for tongue and larynx that is attached to skull at synovial joint and forms base of the larynx.
The bones are: tympanohyoid, stylohyoid, epihyoid, ceratohyoid, basihyoid, thyrohyoid.
Horse has huge stylohyoid – visble in gutteral pouch. Basihyoid has lingual process in tongue.
Larynx is series of 4 types of main cartilages: 1. epiglottis (rests on cd part of soft palate, points rostrally). Epiglottis is made of elastic cartilage, moving passively with pharynx/larynx. Hyoepiglottic ligament attaches epiglottis to baseihyoid. 2. Thyroid cartilage – major part of larynx and made of lamina on either side of floor. Made of hyaline cartilage and less mobile than epiglottis. Thyrohyoid ligament attaches thyroid to hyoid apparatus and thyrohyoid bone (also attached to epiglottis). 3. Cricoid cartilage – most caudal, made of hyaline cartilage, most stable. Cricotracheal ligament attaches it to trachea and cricothyroid ligament to attach to thyroid. 4. Arytenoid cartilage on either side of midline, forming dorsal part of larynx. Two articulating with cricoid. Vocal ligament attaches vocal process to thyroid cartilage. Mixed hyaline and elastic cartilage. Vestibular ligament attaches arytenoid to thyroid.
Caudal to larynx is trachea. There are several mucous membrane folds within larynx. Arytenoepiglottic fold – from epiglottis to arytenoid to form entrance to larynx. Vestibular fold – elevation in larynx wall, lining rostrally. Vocal fold – elevation in larynx wall, lining caudally.
Floor of larynx also has ventral recess.
Additus laryngis – opening of larynx and opens into laryngeal vestibule. Consists of arytenoepiglottic fold, epiglottis, arytenoid cartilage, rimaglottis.
Vagus nerve gives rise to Cranial larnygeal nerve that supplies additus and glottis.
Recurrent laryngeal nerve supplies structures caudal to glottis.
Dorsal cricoarytenoideus rotates arytenoid to abduct folds and tenses vocal folds (opening rima glottis). Lateral cricoarytenoideus – rotates arytenoids to adduct folds to midline – closes rima glottis. Both innervated by recurrent laryngeal n.
Cuneiform process of arytenoid is incorporated into epiglottis, rather than arytenoid. Has both vestibular and vocal folds.
Larynx is fixed in nasopharynx which makes horse obligate nasal breathers.
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