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 301 Part VI, ANA T O M Y. The two crico-arytenoidsei laterales are fmall, and fiThe epiglottis has likewife .two lateral ligaments, by tuated more laterally than the former. Each mufcle is which it,is conne&ed to the arytenoides, all the way.to their points or cornua. It has alfo a membranous liga- fixed by one end to the fide of the broad part of the criment, which running along the middle of its anterior or coides, and by the other to the lower part of the fide concave fide, ties it to the root or bafis of the tongue. of the neighbouring arytenoides. This ligament is only a duplicature of the membrane The two thyro-arytenoidaei are very broad, each rmdwhich covers the epiglottis, continued to the neighbour- cle being fituated laterally between the thyroides and cning parts. Laftly, there are two lateral membranous li- coides. It is fixed by a broad infertion in the infide of gaments belonging to it, -fixed near the glandulous bodies the ala of the thyroid cartilage; and the fibres contracting from thence, run from before backward, and from called amygdala. The epiglottis is -not only perforated by the regular below upward, towards the neighbouring arytenoid carholes already mentioned, but has likewife a great number tilage, in which they are iaferted, from the glottis to the of fmall irregular failures and breaks, which are fo ma- angle of the bafis. ny different lacuna fituated between its two membranes, The arytenoidsei are fraall mufcles lying on the pofteand filled with fmall glands, the excretory orifices of rior concave fides of the arytenoid cartilages, of which two are called crucial arytenoidai, and one tranfverfe. which are chiefly on the backfide of this cartilage. The larynx gives infection to a number of mufcles, The crucial mufcles run each obliquely from the bafis of one arytenoid cartilage, to the middle and upper part which fhall now be defcribed. The fterno-thyroidxi arc two long, flat, narrow, thin of the other, the left mufcle covering the right. mufcles, like ribbons, broader above than below, and fi- The arytenoidasus traafverfalis is inferted more or lefs tuated along that part of the neck which lies between the diredfly, by both extremities, in the two arytenoid carthyroid cartilage and the fternum. They are covered by tilages. the fterno-hyoidaei, and they cover the thyroid glands, The two thyro-epiglottici crofs the thyro-arytenoida?!, being inferted in the inner lateral part of the thyroides, palling immediately before them. Each mufcle is fixed, by its lower extremity, partly in and laterally in the epiglottis. the fuperior portion of the inner or backfide of the fter- The aryteno-epiglottici are fmall flefhy fafciculi, each num, partly in the ligament and neighbouring portion of of which is fixed by one extremity in the head-of one the clavicula, and partly in the cartilaginous portion of of the arytenoid cartilages, and by the other in the nearthe firft rib. Sometimes it runs a great way down on eft edge of the epiglottis. the firfl bone of the fternum, and crofles the mufcle on The larynx ferves particularly to admit and let out the the other fide. From thence it runs up on the afpera matter of refpiration ; and the folidity of the pieces of arteria, clofe by its fellow, pafles before the thyroid which it is compofed hinders not only external objedls, glands, over the cricoid cartilage; and is inferred, by Its but alfo any hard thing which we fwallow, from diforupper extremity, in the lower part of the lateral fide of dering this pafiage. The glottis, being a narrow flit, mothe thyroid cartilage, and partly along that whole fide. difies the air which we breathe; and as it is very eafily The thyro-hyoidaei, or hyo-thyroidaei are two flat, dilated and contradted, it forms the different tones of thin mufcles, lying clofe by each other, between and a- the voice, chiefly by means of the different mufcles inbove the former. Each of them is inferred, by its upper ferted in the cartilagines arytenoidaeae, to which the oextremity, partly in the bafis, and partly in the neigh- ther mufcles of the larynx are afliftants. bouring part of the great cornua of the os hyoides; and The whole larynx is likewife of ufe in deglutition, by by its lower extremity, in the lower part of the lateral means of its connedtion with the os hyoides, to which fide of the thyroid cartilage, immediately above the fu- the digaftric mufcles of the lower jaw adhere; which perior extremity of the fterno-thyroidieus; and both this irufcles raife the larynx together with the os hyoides efuperio/- extremity of the laft named mufcle, and the *ery time we fwallow. lower extremity of the thyro-hyoidaeus, are, at their The facility of varying and changing the tone of the place of union, confounded a little witla the thyro-pha- voice, depends on the flexibility of the cartilages of the ryngaus inferior. larynx, and decreafes in proportion as we advance in The crico-thyroidrei are two fmall mufcles, fituated age, bccaufe thefe cardlages gradually harden and oflify. Obliquely at the lower part of the thyroid cartilage. The mufculi fterno-thyroidan ferve in general to pull They are inferted by their lower extremities in the ante- down the thyroid cartilage, and the whole larynx along rior portion of the cricoid cartilage, near each other, and with it. The thyro-hyoidasi may, as occafion requires, by their fuperior extremities, laterally in the lower edge either draw up the larynx toward the os hyoides, or draw of the thyroid cartilage, at a diftance from each other. that bone downward toward the eartilago thyroides. The two mufculi crieo-arytenoidsei pofteriores are fi- It is difficult to determine the ufe of the crico-thyroituated pofteriorly at the large or back portion of the cri- dsei from their fituation^. They may either pull the cricoides, filling almoft the two longitudinal furfaces of that coides obliquely backward, or the thyroides obliquely portion, and diftinguilhed by the prominent line between forward; thefe two.furfaces. Each of them runs up obliquely, and Both the lateral and pofterior crico-arytenoidsr, may is inferted, by. its ijpper extremity, in the pofterior part of feparate the ary tenoid cartilages, and thereby open or dithe bafis of the arytenoid cartilage-of the fame fide, near late the glottis. the angle of that bafis. The thyro-arytenoidari afling together, draw both the Vox,. I. No. 13. 3 4G arytenoid