Craniofacial Muscles

144 L.A. Vinney and N.P. Connor
Fig. 9.1 Posterior view of canine larynx showing interarytenoid (IA) and posterior cricoarytenoid
(PCA) muscles. Cricoid (CrC), thyroid (TC), and arytenoid (Ar) cartilages, aryepiglottic (AryF)
folds, epiglottis, and piriform sinuses (PS) are also shown. Photograph courtesy of Dr. Seth Dailey
vagus, the tenth cranial nerve (CNX). The CT is innervated by the external branch
of the superior laryngeal nerve that also originates from the vagus nerve.
The TA muscle makes up the main muscular component of the vocal folds and
contributes to vocal fold adduction and tension. The TA is found immediately deep
to the vibrating laryngeal mucosa of the vocal folds and makes up the bulk of the
vocal fold. Typical divisions of the TA muscles are into a more medial thyrovocalis
(or simply “vocalis”) muscle and a more lateral thyromuscularis muscle. Other synonymous
nomenclature is medial or lateral thyroarytenoid muscles, respectively.
The TA muscle components attach to the laryngeal cartilages for which they are
named and provide tension within the vocal folds during phonation. This tension
affects vocal pitch and may oppose the action of the CT or complement it. Although
it is generally thought that the TA is innervated by the recurrent laryngeal nerve of
the vagus, additional innervation from the external division of the superior laryngeal
nerve was found in one canine study (Nasri et al. 1997 ) . There appears to be more
study of the TA than other intrinsic laryngeal muscles, perhaps due to its important
role in voicing and ease of identi fi cation. However, relative to the studies of limb
muscles, the number of TA muscle studies is limited. In a Medline search we
conducted for literature containing a major subject heading of “limb muscle”
between the years 1980 and May 2011, we obtained 1,217 citations, whereas a