DISSECTION OF THE HEAD AND NECK 311 



(aba) Wheat-like or triticeous cartilage (cartilago triticea). 



(b) Cricothyreoid muscle (M. cricothyreoideus}. 



(ba) Straight part (pars recta) (0. T. anterior or oblique part). 



(bb) Oblique part (pars obliqua) (0. T. posterior or horizontal 



part). 



Study its origin, insertion, action, and innervation. 



(c) Middle cricothyreoid ligament (ligamentum cricothyreoideum [me- 



dium]) (0. T. middle portion of cricothyreoid membrane). 

 This is really a part of the conus elasticus (vide infra). 



Reverse position of larynx on wooden block, so that posterior 

 surface looks upward. Slit open oesophagus along middle line 

 behind. Dissect the tunica mucosa cautiously off the posterior 

 aspect of the cricoid and arytaenoid cartilages, avoiding injury 

 to the A. laryngea inferior and N. recurrens (between thyreoid 

 and cricoid cartilages). 



Clean carefully the following muscles and ascertain their 

 form, position, origin, insertion, action, and innervation : 



(a) Posterior cricoarytaenoid muscle (M. cricoarytaenoideus posterior). 



(b) Oblique arytaenoid muscle (M. arytaenoideus obliquus). 



(ba) Aryepiglottic muscle (M. aryepiglotticus) (0. T. aryteno- 

 epiglottidean muscle). 



(c) Transverse arytaenoid muscle (M. arytaenoideus transversus) . 



From this point on, the dissection is conducted differently on 

 the two sides, that on the right being made especially for the 

 muscles, that on the left for the vessels and nerves. 



Fasten larynx by its left side to the wooden block. Remove 

 the M. cricothyreoideus of the right side. Cut through the right 

 ligamentum hyothyreoideum laterale; disarticulate the right 

 inferior cornu of thyreoid cartilage from the facies articularis 

 thyreoidea on the side of the cricoid cartilage. Cut vertically 

 through the lamina dextra of the thyreoid cartilage a little lat- 

 eral from the anterior median line and remove the detached right 

 lamina. 



Clean carefully and study the form, position, origin, inser- 

 tion, action, and innervation of the following muscles : 



(a) Lateral crico-arytaenoid muscle (M. cricoarytaenoideus later alls}. 



(b) Thyreo-arytaenoid muscle (M. thyreoarytaenoideus [externus]). 



(c) Thyreo-epiglottic muscle (M. thyreoepiglotticus) (0. T. thyro-epi- 



glottidean muscle). 



(d) Vocal muscle (M. vocalis) (0. T. internal thyro-arytenoid muscle). 



(This muscle is best seen in a cross-section through the whole 

 larynx at the level of the true vocal cord. It lies medial from the 



