RAVEN. 73 



and the bronchiae ; and the variety of modulation birds in 

 general are known to possess has its corresponding variety 

 of forms and appendages. The glottis, or superior larynx, 

 opens into the mouth at the root of the tongue. The 

 orifice, figure 1, letter 6, in the first group of illustrations, 

 is long and narrow, encircled by two pair of muscles, 

 figure 2, b, b, and figure 3, a, a, which govern the size of 

 the aperture, and constitute one of the accessory means by 

 which the sound of the voice is regulated. Birds have no 

 epiglottis, or covering over this aperture, to prevent any 

 particles of food passing into the windpipe ; but the sur- 

 face near the opening is furnished with numerous papillae, 

 pointing backwards, which assist in directing and convey- 

 ing food towards and into the oesophagus. 



Figure 1 is a representation of the glottis with its sur- 

 rounding membranes. Figure 4 is a representation of the 

 cartilages forming the superior larynx, all the softer parts 

 having been removed. The letters a refer to the principal 

 cartilage, which, when in its natural situation, lies upon 

 the pharyngeal portion, and between the cornua of the os 

 hyoides, or bone of the tongue. This cartilage appears to 

 perform the double office of the thyroid and cricoid car- 

 tilages in the higher animals. In substance it is uniformly 

 thin, its shape nearly triangular when laid flat, one angle 

 placed forward, the lateral angles curving upwards to sup- 

 port the base of the arytenoid cartilage on its own side. 

 The letters b, 6, refer to the arytenoid cartilages, supported 

 at their base by the lateral angles of the cricoid cartilage, 

 before mentioned, and projecting forwards in two narrow 

 and thin parallel processes over two-thirds of the orifice 

 formed by the curved lateral portions of the cartilage un- 

 derneath : each parallel process forming a slight groove on 

 its superior surface by their edges also curving upwards. 



The glottis is closed by a pair of muscles, fig. 3, a, a, 



