ORGANS OF VOICE AND RESPIRATION. 113 



Such a single pair of muscles (m. m. broncho-trachcales) occur 

 in the Rapaces, some Scansores and Picariae, e. g. Picus, Cypselus, 

 Caprimulgus, and, though but feebly developed, in the Cuckoo ; also 

 in the Pigeons (which have a large external membranous fenestra), 

 and many Grallse and Natatores, while it is absent in other Scan- 

 sores and Picariae, e. g. Alcedo, Upupa, other Grallse, and Natatores, 

 as Hcematopus, Anser, Anas, Mergus, and in the Brevipennes and 

 Gallinae. This single pair of muscles often ascends high up close to 

 the sterno-tracheal muscles, draws the bronchi in the direction out- 

 ward and thus expands their glottidean fissures. 



Two special muscles of the larynx do not appear to occur in these 

 cases, to which succeeds the peculiar structure of that organ in the 

 Parrots, where it has three strong pairs of muscles, but the sterno- 

 tracheales are absent. The inferior glottis is single and narrow 

 in the Parrots, from the inferior partition or cross-bone being 

 wanting. The structure of their larynx is as follows : the tra^ 

 chea passes into a short tympanum, and beneath this there is con- 

 stantly situated a semilunar ossified cartilage (cart, semilunaris), 

 having its concavity directed downward, and between its border 

 which excavated in a crescentic form is curved upward, and the first 

 bronchial demi-ring, is situated the external tympaniform mem- 

 brane. The superior semilunar pieces can be moved inward and 

 outward upon the tympanum, or raised and depressed like a pair 

 of valves, and the membrane follows these movements. Of the 

 three muscles, that which is situated most deeply is the shortest ; 

 it arises from the upper part of the tympanum, and is inserted by 

 its whole breadth to the upper semilunar cartilage which is move- 

 able like a valve. This is the 'm. abductor cart, semilunaris, and 

 while this muscle elevates the corresponding semilunar bone, it 

 draws also the membrane outward, and thus widens the opening 

 of the glottis. Above this is situated another longer muscle, which 

 arises close to it, and passing in a bridge-like manner over the tym- 

 paniform membrane, is inserted into the uppermost bronchial ring ; 

 it elevates the bronchus of the corresponding side, by which move- 

 ment the two membranes approximate, come nearly in contact in 

 the middle line, and thus narrow the fissure of the glottis. Above 

 this short levator bronchi, is situated another, the levator longus, 

 which has the same function, though at the same time its muscular 

 belly arises higher up and is continued into a long tendon which, run- 

 ning over that of the former muscle, is occasionally inserted into 

 the anterior side of the fifth to the seventh, or often the third to the 



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