346 AVES. 



entirely closed, it is plain that it cannot be largement of this kind, in which the bony 

 considered as influencing the voice, otherwise rings are entire, and of the same texture as in 

 than by dividing or articulating the notes the rest of the tube. In the Golden-Eye the 

 after they are formed by the lower larynx, trachea is four times larger at the dilatation 

 The superior larynx presents, indeed, but few than at any other part. In the Goosander 

 varieties in the different species of Birds ; and ( Mergus merganser), the trachea presents two 

 these relate chiefly to certain tubercles which sudden dilatations of a similar structure to that 

 are observed in its anterior, but which vary in above described. The trachea of the Emeu 

 number, and do not exist at all in some spe- (Dromaius ater) is also remarkable for a sud- 

 cies, as the singing birds ; being chiefly pre- den dilatation, but in this instance the cartila- 

 sent in those birds which have a rough un- ginous rings do not preserve their integrity at the 

 musical voice. In the Pelecan, the Gigantic dilated part, but are wanting posteriorly, where 

 Crane, and most of the Rasores, a process ex- the tube is completed by the membranes only, 

 tends backwards into the cavity of the upper The bronchi (v, fig. 163) are straight, corn- 

 larynx from the middle of the posterior surface pressed, delicate, and easily lacerable tubes ; 

 of the thyroid cartilage, and seems destined their rings, in most Birds,* form only a small 

 to give additional protection to the air-passage, segment of a circle, and are situated at the 



The trachea (G, jig. 170, 171) in Birds is outer side of the tube, which is convex; the 

 proportionally longer, in consequence of the inner side is completed by a membrane (mem- 

 length of the neck, than in any other class of brana tympaniformis) extended between the 

 animals, its length being further increased in extremities of the defective rings, and is flat, 

 many species by convolutions varying in extent The bronchial rings are weak and thin ; in 

 and complexity. A species of Sloth (Bradypus Birds without true muscles of voice, they are 

 tridactylus) among Mammalia, and a species of either of uniform thickness, or become gradually 

 Crocodile ( Crocodilus acutus) among Reptiles, thinner to their termination: in many Birds 

 present an analogous folding of the trachea. which have the vocal muscles they grow sud- 



The trachea is composed in Birds of a denly thinner below the insertion of those 



series of bony, and sometimes, as in the muscles : this is remarkable in Owls. 



Ostrich, of cartilaginous rings, included be- The muscles of the trachea are generally a 



tween two membranes. In those cases in single pair, the sterno-tracheales, to which, in 



which they are of a bony structure, the ossi- some cases, a second pair is added, the cleido- 



fication is observed to commence at the anterior tracheales. The sterno-tracheales, which are 



part of each ring, and gradually to extend on analogous to the sterno-thyroidei of mammalia, 



both sides to the opposite part. arise from the costal processes of the sternum, 



The tracheal rings, whether bony or cartila- and ascend along the sides of the trachea, as 



ginous, are, with the exception of the two far in general as the superior larynx. The 



uppermost, always complete, and not, as in cleido-tracheales (ypsilo-tracheens of Cuvier) 



most quadrupeds, where the windpipe bears a arise from the furculum or conjoined clavicles, 



different relation to the organ of voice, defi- and pass along the sides of the trachea parallel 



cient posteriorly. They differ in shape, being to the preceding. 



sometimes more or less compressed. They Many birds possess only the tracheal and 



are generally of uniform breadth, but in some superior laryngeal muscles, and have no proper 



species are alternately narrower at certain parts muscles of the inferior larynx. Cuvierf divides 



of their circumference and broader at others, such birds into those which have the lower 



and in these cases the rings are generally larynx simple or without dilatations, as the 



closely approximated together, and, as it were, Rasores, and into those which have lateral 



locked into one another. This structure is bony cavities at that part, as the males of the 



most common in the Grallatores, where the Genus Anas, Cuv. and Mergus. 



rings are broadest alternately on the right and His next division in the order of complexity 



left sides : the French Academicians have given of the vocal organs includes those birds which 



a good illustration of this structure from the have one pair of vocal or inferior laryngeal 



trachea of the Demoiselle Crane. muscles, the Broncho-tracheales ; these arise 



With respect to the diameter of the tracheal from the sides of the lower part of the trachea, 



rings, this may sometimes be pretty uniform and are inserted in one of the half-rings of the 



throughout, and the trachea will consequently bronchi at a less or greater distance from the 



be cylindrical, as in the Insessores, the Gralla- lower larynx in different birds ; as, for exam 



tores which have a shrill voice, the females of pl e , in the first half-ring in the Genus Falco, 



the Natatores, and most Raptores and Ra- in most of the Grallatores, in the Genus 



sores : or the rings may gradually decrease in Larus (Gull), and Phalacrocorax (Cormo- 



diameter, forming a conical trachea, as in the rant); in the third half-ring in the King-fisher 



Turkey, the Heron, the Buzzard, the Eagle, (Alcedo), and Goat-sucker ( Caprimulgus) ; 



the Cormorant, and the Gannet; or they may in the fifth half-ring in the Genus Ardea, Cuv. 



become wider by degrees to the middle of the in the Cuckoo and the Eagle-Owl (Bubo 



trachea, and afterwards contract again to the maximus) ; in the seventh half-ring in the 

 inferior larynx ; or, lastly, they may experience 



sudden dilatations for a short extent of the . T , ... . 



.1 r-> u / * i i \ ,1 * In the Vultures, which have no true vocal 



trachea ; the Golden-eye (Anas clangula), the muscles> but onl the * sterno-tracheales, the first four 



Velvet-duck (Anas Jusca), and the Mergan- bronchial rings are entire, 



ser CMergns serrntor), present a single en- t Anat. Comparec, torn. iv. p. 450. 



