346 



AVES. 



entirely closed, it is plain that it cannot be 

 considered as influencing the voice, otherwise 

 than by dividing or articulating the notes 

 after they are formed by the lower larynx. 

 The superior larynx presents, indeed, but few 

 varieties in the different species of Birds ; and 

 these relate chiefly to certain tubercles which 

 are observed in its anterior, but which vary in 

 number, and do not exist at all in some spe- 

 cies, as the singing birds ; being chiefly pre- 

 sent in those birds which have a rough un- 

 musical voice. In the Pelecan, the Gigantic 

 Crane, and most of the Rasores, a process ex- 

 tends backwards into the cavity of the upper 

 larynx from the middle of the posterior surface 

 of the thyroid cartilage, and seems destined 

 to give additional protection to the air-passage. 

 The trachea (G,Jig. 170, 171) in Birds is 

 proportionally longer, in consequence of the 

 length of the neck, than in any other class of 

 animals, its length being further increased in 

 many species by convolutions varying in extent 

 and complexity. A species of Sloth (Bradypus 

 tridactylus) among Mammalia, and a species of 

 Crocodile (Crocodilus acutus) among Reptiles, 

 present an analogous folding of the trachea. 



The trachea is composed in Birds of a 

 series of bony, and sometimes, as in the 

 Ostrich, of cartilaginous rings, included be- 

 tween two membranes. In those cases in 

 which they are of a bony structure, the ossi- 

 fication is observed to commence at the anterior 

 part of each ring, and gradually to extend on 

 both sides to the opposite part. 



The tracheal rings, whether bony or cartila- 

 ginous, are, with the exception of the two 

 uppermost, always complete, and not, as in 

 most quadrupeds, where the windpipe bears a 

 different relation to the organ of voice, defi- 

 cient posteriorly. They differ in shape, being 

 sometimes more or less compressed. They 

 are generally of uniform breadth, but in some 

 species are alternately narrower at certain parts 

 of their circumference and broader at others, 

 and in these cases the rings are generally 

 closely approximated together, and, as it were, 

 locked into one another. This structure is 

 most common in the Grallatores, where the 

 rings are broadest alternately on the right and 

 left sides : the French Academicians have given 

 a good illustration of this structure from the 

 trachea of the Demoiselle Crane. 



With respect to the diameter of the tracheal 

 rings, this may sometimes be pretty uniform 

 throughout, and the trachea will consequently 

 be cylindrical, as in the Insessores, the Gralla- 

 tores which have a shrill voice, the females of 

 the Natatores, and most Raptores and Ra- 

 sores: or the rings may gradually decrease in 

 diameter, forming a conical trachea, as in the 

 Turkey, the Heron, the Buzzard, the Eagle, 

 the Cormorant, and the Gannet ; or they may 

 become wider by degrees to the middle of the 

 trachea, and afterwards contract again to the 

 inferior larynx ; or, lastly, they may experience 

 sudden dilatations for a short extent of the 

 trachea; the Golden-eye (Anasclangula), the 

 Velvet-duck (Anas fusca), and the Mergan- 

 ser (Mergus sermtor), present a single en- 



largement of this kind, in which the bony 

 rings are entire, and of the same texture as in 

 the rest of the tube. In the Golden-Eye the 

 trachea is four times larger at the dilatation 

 than at any other part. In the Goosander 

 ( Mergus merganser), the trachea presents two 

 sudden dilatations of a similar structure to that 

 above described. The trachea of the Emeu 

 (Dromaius ater) is also remarkable for a sud- 

 den dilatation, but in this instance the cartila- 

 ginous rings do not preserve their integrity at the 

 dilated part, but are wanting posteriorly, where 

 the tube is completed by the membranes only. 

 The bronchi (v, jig. 163) are straight, com- 

 pressed, delicate, and easily lacerable tubes; 

 their rings, in most Birds,* form only a small 

 segment of a circle, and are situated at the 

 outer side of the tube, which is convex ; the 

 inner side is completed by a membrane (mem- 

 brana tympaniformis) extended between the 

 extremities of the defective rings, and is flat. 

 The bronchial rings are weak and thin ; in 

 Birds without true muscles of voice, they are 

 either of uniform thickness, or become gradually 

 thinner to their termination : in many Birds 

 which have the vocal muscles they grow sud- 

 denly thinner below the insertion of those 

 muscles : this is remarkable in Owls. 



The muscles of the trachea are generally a 

 single pair, the sterno-tracheales, to which, in 

 some cases, a second pair is added, the cleido- 

 tracheales. The sterno-tracheales, which are 

 analogous to the sterno-thyroidei of mammalia, 

 arise from the costal processes of the sternum, 

 and ascend along the sides of the trachea, as 

 far in general as the superior larynx. The 

 cleido-tracheales (ypsilo-tracheens of Cuvier) 

 arise from the furculum or conjoined clavicles, 

 and pass along the sides of the trachea parallel 

 to the preceding. 



Many birds possess only the tracheal and 

 superior laryngeal muscles, and have no proper 

 muscles of the inferior larynx. Cuvierf divides 

 such birds into those which have the lower 

 larynx simple or without dilatations, as the 

 Rasores, and into those which have lateral 

 bony cavities at that part, as the males of the 

 Genus Anas, Cuv. and Mergus. 



His next division in the order of complexity 

 of the vocal organs includes those birds which 

 have one pair of vocal or inferior laryngeal 

 muscles, the Broncho-tracheales ; these arise 

 from the sides of the lower part of the trachea, 

 and are inserted in one of the half-rings of the 

 bronchi at a less or greater distance from the 

 lower larynx in different birds ; as, for exam 

 pie, in the first half-ring in the Genus Falco, 

 in most of the Grallatores, in the Genus 

 Larus (Gull), and Phalacrocorax (Cormo- 

 rant) ; in the third half-ring in the King-fisher 

 (Alcedo), and Goat-sucker ( Caprimulgus ) ; 

 in the fifth half-ring in the Genus Ardea, Cuv. 

 in the Cuckoo and the Eagle-Owl (Bubo 

 maximus); in the seventh half-ring in the 



* In the Vultures, which have no true vocal 

 muscles, but only the sterno-tracheales, the first four 

 bronchial rings are entire. 



t Anat. Comparee, torn. iv. p. 450. 



