DISSECTION OF THE DOG 170 



for later examination. Sever the union of one thyroid cornu with the 

 hyoid bone, and cut through the hyo-thyroid ligament on the same side 

 as far as the middle line. Disarticulate the aboral thyroid cornu from 

 the cricoid cartilage and make a longitudinal incision through the thyroid 

 lamina a little distance from the middle line. Cut across the crico- 

 thyroid muscle. Now carefully remove the isolated piece of thyroid 

 cartilage. Clean the three muscles thus exposed to view, and define the 

 appendix of the laryngeal ventricle. 



M. CRico-ARYT^NOiDEtrs lateealis. — The lateral crico-arytenoid muscle 

 is much smaller than the dorsal muscle of the same name. Triangular in form, 

 its origin is from the oral border of the arch of the cricoid, and its insertion into 

 the muscular process of the arytenoid cartilage. 



M. vocalis. — Running parallel to the vocal fold is the thick vocal 

 muscle. The fibres composing it arise from the medial surface of the thyroid 

 lamina close to the middle line, and from the strong crico-thyroid ligament. 

 They are inserted into the muscular process and lateral surface of the aryte- 

 noid cartilage, some of them being apparently continuous with the dorsal 

 crico-arytenoid muscle. 



M. ventrictjlaris. — The ventricular muscle is oral to and shorter than 

 the preceding. The fibres of the muscle pass from the broad basal part of the 

 cuneiform cartilage to the arytenoid and inter- arytenoid cartilages. 



If the vocal muscle be released from its thyroid attachment and turned 

 aside, a thin membrane connected with the oral border of the cricoid cartilage 

 will be exposed. The membrane ventrally is continuous with the crico- 

 thyroid ligament, and dorsally reaches the vocal process of the arytenoid 

 cartilage. Its oral border joins the vocal ligament (ligamentum vocale), a 

 definite band stretching from the angle of union of the laminae of the thyroid 

 cartilage to the vocal process of the arytenoid cartilage. The vocal ligaments 

 are covered by the vocal folds of mucous membrane already examined in 

 connection with the interior of the larynx ; and, like the folds, are close together 

 at their ventral ends, but diverge towards their arytenoid attachments. 



Appendix ventrictjli laryngis. — The appendix of the laryngeal ventricle 

 is a spacious blind diverticulum which will be found oral to the vocal ligament, 

 and between the thyroid lamina and the vocal muscle laterally and the cunei- 

 form and arytenoid cartilages and the ventricular muscle medially. The 

 appendix generally extends as far as the oral border of the thyroid lamina. 



Dissection. — An examination may now be made of the lateral wall of the 

 cavity of the larynx. This is rendered easier by the removal of that 

 part of the ary-epiglottic fold which joins the cuneiform cartilage to the 

 epiglottis. 



The ventricle of the larynx can best be studied at this stage of the dissection. 

 It is an elongated depression, bounded aborally by the vocal fold and 



n2 



