1 ORGANS OF RESPIRATION AND VOICE. 173 



A true cartilaginous epiglottis is found to be present either as a nar- 

 row papilla, or broader lobule, in different Serpents and Sauria. The 

 vocal ligaments are not nearly so generally present among the Squami- 

 gera, as the Anourous Batrachia. They are wanting in all the 

 Serpents, the hissing sounds of these animals being produced like 

 the act of whistling in the human subject, by the edges of the narrow 

 laryngeal outlet performing friction against the air in expiration. 

 The Lizards possess a pair of narrow vocal chords. A thick fold of 

 mucous membrane with a subjacent pouch is all that is to be remarked 

 in the Crocodile. 



A peculiar structure in the genus Chameleo, reminding us of the 

 laryngeal pouches in many Apes, is well deserving of notice. Be- 

 tween the larynx and first treacheal ring is found an opening which 

 leads into a membranous sac that can be distended with air. 



As concerns the Laryngeal muscles, an expansor of the glottis (m. 

 dilatator aditus laryngis Henle) is found, very generally in the Ba- 

 trachia, and arises either from the vertebral column and the skull, 

 or from the lingual bone (this being the case in all the Anoura), and 

 is inserted into the edge of the vocal fissure, or into the cartilago 

 lateralis of its corresponding side. Besides this muscle, in examples 

 of a more perfect structure, we may distinguish three others, a di- 

 lator of the laryngeal inlet, with a contractor and a compressor of the 

 cavity of the larynx, all of which exhibit manifold diversities. 

 Among the Squamigera an elevator and a depressor of the larynx are 

 found in the Serpents, as a pair of long muscles, that are absent in the 

 higher orders of the sub-class, but a compressor and dilatator aditus 

 laryngis are universally present. 



In some of the Anourous Batrachia, e. g., in the Tree and Meadow 

 Frogs (Hyla and Rana esculenta), but not in R., temporaria, accessory 

 organs are associated with the vocal apparatus. They consist of a 

 pair of thin-walled, very dilateable bladders, situated by the articu- 

 lating surface of the inferior maxilla, and which open always into 

 the cavity of the mouth below the Eustachian tubes ; they contrib- 

 ute to strengthen the voice, by serving as an apparatus of reso- 

 nance. 



Between the carotid arteries and resting upon the trachea, a small 

 vascular gland, which may be viewed as the analogue of the Thyroid 

 gland, is found in several Squamigerous Reptiles, as in the Tortoises, 

 Crocodiles, and also in the Serpents. 



