DISSECTION OF THE DOG 175 



It would be well that the student procure a set of disarticulated laryngeal 

 cartilages in order that he may familiarise himself with their peculiarities 

 before commencing the actual dissection of the organ. Seeing that it is well- 

 nigh impossible to obtain an intelligent grasp of the arrangement of the muscles, 

 etc., without knowing something of the parts with which they are connected, 

 an account of the laryngeal cartilages is given here instead of later. 



Cartilagines laryngis. — The larynx of the dog contains three single 

 cartilages — thyroid, cricoid, and epiglottis ; and three paired — arytenoid, 

 corniculate, and cuneiform. 



Cartilago thyreoidea. — The thyroid cartilage is the largest and consists of 

 two laminae meeting and fusing in the mid-ventral line at the laryngeal pro- 

 minence (prominentia laryngea). The dorsal border of each lamina terminates 

 in two projections or cornua, the oral of which (cornu craniale) is connected 

 with the thyro-hyal bone, while the aboral (cornu caudale) articulates with 

 the cricoid cartilage. 



The oral border of the two laminae is connected with the hyoid bone by 

 the hyo-thyroid ligament (ligamentum hyo-thyreoideum). Aborally the laminae 

 bound a notch (incisura thyreoidea caudale) and are joined to the cricoid 

 cartilage by the crico-thyroid ligament (ligamentum crico-thyreoideum). The 

 lateral surface is crossed by a faint oblique line (linea obliqua) to which the 

 sterno-thyroid and thyro-hyoid muscles are inserted. 



Cartilago cricoidea. — The cricoid cartilage is placed aboral to the thyroid, 

 by the laminae of which it is partially covered laterally. In form it has some 

 resemblance to a signet ring, and may be divided into a ventral arch and a 

 broader dorsal portion or lamina. In the middle line of the oral border there 

 is a shallow notch, and on each side of this an oval, convex facet for articulation 

 with an arytenoid cartilage (facies articularis ary taenoidea) . On the dorsal 

 surface of the lamina there is a median ridge. 



Cartilagines arytcenoidece. — Resting on the oral border of the lamina of the 

 cricoid cartilage are the two irregularly pyramidal arytenoid cartilages. The 

 apex of each is directed oralwards and is continued by a curved piece of elastic 

 structure which constitutes the corniculate cartilage (cartilago corniculata). 

 The base of the arytenoid cartilage has a prominent ventral angle, the vocal 

 process (processus vocalis) to which the vocal fold is attached, and a lateral 

 angle, the muscular process (processus muscularis). on which certain muscles 

 terminate. A small, nodular interarytenoid cartilage lies over the narrow gap 

 between the two arytenoid cartilages. 



Cartilago epiglottica. — The epiglottis is a four-sided plate of elastic cartilage 

 connected with the thyroid by a narrow stem (petiolus epiglottidis). The 

 oral angle of the plate is free and projects towards the base of the tongue ; 

 while the lateral angles form marked projections connected, by means of 

 folds of mucous membrane, with the cuneiform cartilages. Of the two surfaces 

 the dorsal is entirely free and covered by mucous membrane. The ventral 



