Anatomy of Birds
Avian medicine is an important interest of the veterinary profession. It comprises two significantly different branches, one concerned with disease control in commercial flocks of the half dozen species of domestic poultry and the other with the treatment of the much larger variety of cage, aviary, and zoo birds; frequently, some of the latter group are treated as individual patients.
In addition, rehabilitation of wild birds, most notably oiled seabirds and injured raptors, is rapidly increasing. This chapter seeks to supply practitioners working in poultry medicine with a basic knowledge of anatomy sufficient for the understanding of the special features of poultry physiology and pathology, including that required for the conduct of postmortem examinations. It is based on the chicken, and most data and illustrations refer to that species. Some details relevant to the growing number of veterinarians concerned with the examination and treatment of companion and exotic birds are included, but reference must be made to specialist works for more comprehensive treatment of such matters.Birds evolved from reptiles and retain many reptilian features: scales on their beaks, legs, and feet; a single occipital condyle; a single middle ear bone (columella); and a complex construction of the jaws. They also have nucleated erythrocytes and a renal portal system and excrete uric acid. They range in size from the ostrich, weighing more than 100 kg, to tiny species like the wren. They owe their extreme evolutionary success to the acquisition of the power of flight, which has enabled them to disperse ubiquitously and adapt to more niches than any other class of vertebrate. However, the anatomical requirements for flight are so rigid that the variation in morphology among all species is less than that found in the mammalian order Carnivora. Flight is so highly demanding metabolically that anatomical or physiological modifications or both are present in nearly every body system. These increase energy output and stability and decrease body weight and wind resistance. They range from the grossly visible, as in the loss of heavy teeth and masticatory musculature, to the microscopic, as in the airways of the lung and the arrangement of conduction fibers in the heart. Together, these specializations render birds at once singularly uniform and strikingly diverse.