CARTILAGES OF THE LARYNX (Fig. 104).--There are three unpaired cartilages, the =thyroid= (1), =cricoid= (3), and =epiglottic= (2), and two paired cartilages, the =arytenoids= (4). [Illustration: FIG. 104.--CARTILAGES OF LARYNX, WITH SIDE VIEW OF HYOID BONE. _b_, ceratohyal; _c_, epihyal; _d_, stylohyal; _e_, tympanohyal; _f_, thyrohyal. 1, thyroid cartilage; 2, epiglottis; 3, cricoid cartilage; 4, arytenoid cartilage; 5, cricothyroid ligament; 6, thyrohyoid ligament; 7, trachea.] The =thyroid= cartilage (=cartilago thyreoidea=) (1) has nearly the form of a visor of a cap, but is relatively broader at its ends than a cap visor. It forms about two-thirds the circumference of a circle, and is so situated that it embraces the other cartilages ventrally and laterally. Its caudal and cranial borders are oblique to its caudocranial axis and are directed dorsocaudad. To the middle of the cranial border is attached the epiglottic cartilage (2), and the whole cranial margin is connected by membrane (6) to the body and caudal cornua (_f_) of the hyoid bone. The dorsal border projects craniad into a considerable cornu which is attached to the free end of the caudal hyoid cornu (_f_). The border also projects caudad into a process which articulates with a facet on the lateral surface of the cricoid cartilage (3). In the middle of the dorsal surface is a longitudinal ridge for attachment of the vocal cords and origin of the thyroarytenoid muscles (Fig. 105, _d_), and at the caudal end of this ridge the caudal border presents a considerable rounded notch. The =cricoid cartilage= (=cartilago cricoidea=) (3) has the form of a seal ring with its broader part dorsad. The broad dorsal part of the ring is partly embraced by the wings of the thyroid cartilage (1). Its caudal border is undulating and nearly at right angles to its caudocranial axis. It is connected by membrane with the first tracheal ring. The cranial border is oblique to the long axis and lies in a plane which passes from the ventral side craniodorsad. Near the median line on each side it articulates by an oblique facet with one of the two arytenoid cartilages (4). Near the midventral line the cricothyroid ligament (5) is attached and it stretches thence to the midcaudal notch of the thyroid cartilage (1). The outer surface presents at the middle of each side a facet for articulation with the thyroid, and is marked in the median dorsal line by a ridge for the posterior cricoarytenoid muscle (Fig. 105, _b_).