AVES. 



265 



1770. FothcrgiU, New inquiry into the suspension 

 of vital action, &c. 8vo. Lond. 1795. Caillau, 

 Mem. surl'asphyxie par submersion, 8vo. Bordeaux, 

 1799. Fine, De la submersion, 4to. Paris, 1805. 

 Berger, Essai sur la cause de 1'asphyxie par sub- 

 mersion, 4to. Paris, 1805. Ploucquet, Animadvers. 

 in statum ac tlierap. submersorum, 4to. Tubing. 

 1799. Hunter, Animal rcconomy, 4to. Leroy, 

 Kccherchcs sur les asphyxies, 8vo. Paris, 1829. 

 Deoergie, Diet, de Med. et Chir. Prat., art. As- 

 phyxie. Royet, in Cyclopaedia of Practical Medi- 

 cine, art. Asphyxia. Kay, on asphyxia, 8vo. Lond. 

 1834 (the most complete and able work on this subj ct 

 in the English language). Edwards, Sur Finfluence 

 des agens physiques, Englished by Drs. Hodgkin 

 and Lister. Appendix, p. 463. 



( W. P. Alison.) 



AVES, birds; (Gr. Ogj0s?; Fr. Oiseaux ; 

 Germ. Vogeln; Ital. Uccelli :) a class of ovi- 

 parous vertebrate animals, with warm blood, 

 a double circulation, and a covering of feathers. 



Birds are organized for flight, and as this, 

 the most vigorous kind of locomotion, demands 

 the greatest energy in the contractility of the 

 muscular fibre, so the respiratory function finds 

 its highest development in the present class. 

 Not only the ramifications of the pulmonary 

 artery, but many of the capillaries of the sys- 

 temic circulation, from the singular extension 

 of the air-cells through the body, are sub- 

 mitted to the influence of the atmosphere, and 

 hence birds may be said to enjoy a double re- 

 spiration. 



Although the heart resembles in some parti- 

 culars that of the Reptilia, the four cavities are 

 as distinct as in the Mammalia, but they are 

 relatively stronger, their valvular mechanism is 

 more perfect, and the contractions of this organ 

 are more forcible and frequent in Birds in ac- 

 cordance with their more extended respiration 

 and their more energetic muscular actions. 



As Birds exceed Mammals in the activity 

 of those functions on which the waste and 

 renovation of the general system more imme- 

 diately depend, so they possess a higher stan- 

 dard of animal heat: their ordinary tempera- 

 ture is 103 and 104, and according to Cam- 

 per is occasionally as high as 107 Fahr. 



The modification of the tegumentary cover- 

 ing characteristic of the present class is to be 

 regarded rather as dependent upon, than oc- 

 casioning, this high degree of internal tem- 

 perature, which requires for its due mainte- 

 nance against the agency of external cold an 

 adequate protection of the surface of the body 

 by means of non-conducting down and imbri- 

 cated feathers ; and this warm clothing is more 

 especially required to meet the sudden vari- 

 ations of temperature to which the bird is 

 exposed during its rapid and extensive flights. 



The generative product is always excluded 

 from the oviduct in an undeveloped state, in- 

 closed, in a liquid form, within a calcareous 

 case or shell. The female organs are, therefore, 

 developed only on the left side of the body. 

 The ovum is subsequently perfected by means 

 of incubation, for which action the bird is es- 

 pecially adapted by its high degree of animal 

 heat. 



Birds form the best characterized, most dis- 



tinct, and natural class in the whole animal 

 kingdom, perhaps even in or ganic nature 

 They present a constancy in their mode of 

 generation and in their tegumen tary covering, 

 which is not met with in any other of the 

 vertebrate classes. No species of Bird ever 

 deviates, like the Cetacea among Mammals, 

 the Serpents among Reptiles, and the Eels 

 among Fishes, from the tetrapodous type of 

 formation which so peculiarly characterizes the 

 vertebrate division of animals. 



The anterior extremities are invariably con- 

 structed according to that plan which best adapts 

 them for the actions of flight; and although, in 

 some few instances, the development of the 

 wings proceeds not so far as to enable them to 

 act upon the surrounding atmosphere with suffi- 

 cient power to overcome the counteracting 

 force of gravity ; yet, in these cases they assist, 

 by analogous motions, the posterior extremities; 

 either, as in the Ostrich, by beating the air 

 while the body is carried swiftly forward by the 

 action of the powerful legs ; or, as in the Pen- 

 guin, by striking the water after the manner of 

 fins, and by the resistance of the denser- me- 

 dium carrying the body through the water in a 

 manner analogous to that by which the birds 

 of flight are borne through the air. In a few 

 exceptions only are the wings reduced to mere 

 weapons of offence, as in the Cassowary and in 

 the singular Apteryx of New Zealand, in which 

 they are represented by a single spur. In no 

 instance do the anterior extremities take any 

 share in stationary support or in prehension. 



Birds are therefore biped, and the ope- 

 rations of taking the food, cleansing the 

 plumage, &c. are almost exclusively performed 

 by means of the mouth, which consists of two 

 unlabiate and edentate mandibles, sheathed 

 with horn. To facilitate the prehensile and 

 other actions thus transferred to the head, the 

 neck is elongated, and the body generally in- 

 clined forwards and downwards from the hip- 

 joints. The thighs are accordingly extended 

 forwards at an acute angle from the pelvis to- 

 wards the centre of the trunk, and the toes are 

 lengthened and spread out to form an adequate 

 base of support. The actions of perching, 

 walking, running, scratching, burrowing, wa- 

 ding, and swimming, require for their perfect 

 performance different modifications of the pos- 

 terior extremities. The mandibles, again, present 

 as many varieties of form, each corresponding to 

 the nature of the food, and in some degree in- 

 dicative of the organization necessary for its 

 due assimilation. Ornithologists have, there- 

 fore, founded their divisions of the class chiefly 

 on the modifications of the bill and feet. Since, 

 however, Birds in general are associated to- 

 gether by characters so peculiar, definite, and 

 unvarying, it becomes in consequence more 

 difficult to separate them into subordinate 

 groups, and these are necessarily more arbi- 

 trary and artificial than are those of the other 

 vertebrate classes. 



A binary division of the class may be found- 

 ed on the condition of the newly-hatched 

 young, which in some orders are able to run 

 about and provide food for themselves the mo- 



