Batrachia. — In the Batrachia the two arytenoid cartilages form a considerable por tion of the frame of the larynx, and the cri coid, with a few exceptions, is a complete ring. The arytenoids are triangular, and their apices being upwards form the superior lateral boundaries of the larynx. The vocal cords pass from end to end of the bases of the triangles. According to Henle, the whole of the tailless Batrachia, except the Pipa and the Dac tylethro, have vocal cords. In Bufo there are two pairs of vocal cords (fig. 919), correspond ing to the inferior vocal cords in Mammalia.
Above and below the vocal cords there are sacs lined with mucous membrane, and bounded by the arytenoid cartilages. Between the vocal cords a small cartilage is sometimes found.
In Bombinator ignews, Hyla vorucosa, and others, the arytenoid cartilages are regular obtuse-angled, and nearly equilateral triangles. In B. einereus they are more acute-angled, and directed backwards. The vocal cords in bufo are very thin elastic membranes, such as might be expected to produce the croaking deep tones of these batrachia.
In Pipa the larynx is a very peculiar piece of mechanism ; the arytenoid cartilages being convex externally and concave internally, so that when the entrance to the larynx is closed they form a dome over the windpipe, which Cuvier has compared to a kettle-drum.
In Ranatemporarin,R.esculenta, and Hyla, the males are provided with two sacs, which open by a straight canal into the larynx. These sacs are situated on each side of the lower jaw, and are capable of considerable distension, when filled with air during the cry of the animal. Cuvier, Roesel, and Blurnenbach, describe only one sac in Hyla ; but Meckel, as well as Henle and myself, found two sacs, as in the other frogs. These sacs doubt less exert a powerful influence on the quality of the sounds which frogs utter, analogous to the influence of similar sacs which exist in many of the higher animals.
In Proteus anguinus the most simple form of cartilaginous larynx is found, consisting of lateral cartilaginous strips, divided in two on each side ; the superior portion answering to the arytenoid cartilage of the higher orders of animals, the inferior to the laryngo-trachealis cartilages.
In the Triton, and Salamander, the larynx consists of a membranous sac, which is kept open by the lateral cartilages of the vocal tube. Hence we learn that the arytenoid cartilages do not wholly disappear, until the larynx be comes entirely membranous.