VOICE. 



1503 



In Bombmator igncus, Hyla varitcosa, and 

 others, the arytenoid cartilages are regular 

 obtuse-angled, and nearly equilateral triangles. 

 In B. cinereus they are more acute-angled, and 

 directed backwards. The vocal cords in bnfo 

 are very thin elastic membranes, such as might 

 be expected to produce the croaking deep 

 tones of these batrachia. 



In Plpa 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 Rana temporaria, 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 Blumenbach, 

 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. 



Fig. 920. 



In Proteus angtiinus 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. 



INSECTA. A large number of insects are 

 mute; some produce their sounds merely by 

 friction, and others by the passage of the air 

 through the thoracic spiracles. The sounds 

 produced by friction are denominated stridu- 

 lation ; those by the air from the tracheae, 

 buzzing, or humming (bourdonnement), &c. 

 Organs adapted to produce stridulation are 

 found in the Orthoptera, Oinoptera, and some 

 of the Coleoptera. 



Grylli. In the Grylhts camjiestris (fig. 921) 

 the elytrum is composed of dry, thin, trans- 

 lucent membranes, forming two planes, united 

 and strengthened at their junction by four 

 longitudinal and parallel nervures ; one of 

 these planes lies on the back, and the other 

 on the side of the insect. The former 

 of these planes is divided 



Rana temporaria. 



a, tongue ; I, os hyoides ; c, superior vocal cords ; 

 d, inferior vocal cords; e, pharynx; /, right 

 bronchus. 



The muscles acting on the larynx in Batra- 

 chia are the dilator aditus laryngis and the 

 constrictor aditus. Besides these, there is 

 found in the tailless Batrachia a third muscle, 

 the compressor glottidis, which in Brito arises 

 from the columella*, and is inserted into the 

 posterior point of the arytenoid cartilage. Its 

 use is to compress the larynx, to bend the 

 posterior angle of the arytenoid outwards, and 

 to expand the vocal ligament. It is the most 

 important muscle connected with the voice in 

 the tailless Batrachia. Its course varies in 

 different species, and is absent altogether in 

 Pipa. 



* One of the inferior processes of the os hyoides. 



regularly curved nervures, 



by a series of 

 into a number 

 apparatus may 



of areoles. The musical 

 be divided into two systems, the first com- 

 posed of four oblique nervures, which ter- 

 minate in a strong nervure, serrated like a 

 file () ; this may be considered as the bow. 

 The second is formed of three nervures, which 

 take their origin in a remarkable point in the 

 internal border of the elytrum, furnished with 

 a tuft of short stiff hairs, or brush (6); above 

 this point is found a firm, transparent, and 

 nearly triangular disc or sounding plate *, 

 surrounded by a nervure. When the insect 

 cries, the wings are crossed, and the bow 

 rubbed rapidly across the whole length of the 



1. 



Fig. 921. 



2. 



Elytra of Gryllus campestris. 



disc or sounding plate, whereby the whole of 

 both elytra are put in a state of vibration, and 

 the stridulous sounds peculiar to these grylli 

 result. The pitch of the sound of the house 

 cricket is very acute, being equivalent to about 

 4090 vibrations in a second. 



Cicada?, C/gfilas. The Cicada; have their 

 musical instruments inclosed in the interior 

 of the abdomen. Reaumur gives a detailed 

 description, illustrated by drawings, by which 

 they may readily be recognised. These in- 

 struments, he says, are contained in the abdo- 



* Termed by M. Gourean the "chanterelle." 



