Comparative Anatomy - ZOO 420 2(1+1) Zoology Department Dr. Elsayed Younis

The skeleton of the birds includes some unique features The Skeleton of Birds The skeleton of the birds includes some unique features - Many of these features related to the bird's need to be light enough to fly while still maintaining the needed body support. - A lightweight skeleton made of mostly thin and hollow bones. - Most of the bones are pneumatic, meaning they are hollow and filled with air spaces - Birds have a fewer total number of bones than mammals or reptiles. - Many bones have fused together making the skeleton more rigid. - Birds are the only vertebrate animals to have a keeled breastbone

The skeleton of birds looks similar to that of mammals, but there are some important differences. The axial skeleton The skull :- is the skeleton of the head. It passes through three developmental stages ( membranocranium, chondro- cranium and osteocranium ). The bones of the skull are generally fused providing protection to the brain while being of light weight.

The size of the skull is proportionally small when compared to the skulls of other species because a large head would make flying difficult. The skull has large orbits, as sight is an important sensory mechanism for birds. As birds have immobile eyes, head movement and flexibility is required to focus on objects at various distances. A light, toothless beak replaces the bony, heavy toothed jaw of reptiles. Beaks, of course, can be highly modified for different types of food and feeding behavior.

The vertebral column is differentiated into five regions ( cervical, thoracic, lumbar, sacral and caudal vertebrae. The vertebrae are all built up on the same plan, and resemble each other very closely. ( vertebra usually consists of centrum, neural arch, neural foramen, neural spine and transverse processes). Except the first two vertebrae (atlas and axis) which modified to help in the rotation of the head on the neck. Birds have more cervical vertebrae (neck) than many other animals; most have 13 to 25 vertebrae.

The ribs of the thoracic vertebrae include the uncinate process, which giving strength to the rib cage so that it does not collapse during flight. The lumber & sacral vertebrae fused together as well as with the last thoracic. All of these moreover fused with the pelvic girdle to form the synsacrum Some of the caudal vertebrae are free while the others are fused to form a structure called a pygostyle

The sternum is very large and extends far back under the greater part of the abdomen. The sternum : a keel-shaped sternum (breastbone) is where the powerful flight muscles attach to the body. The sternum attached to the pectoral girdle and ribs of the thoracic vertebrae.

The appendicular skeleton pectoral girdle :- consists of two symmetrical halves, each half consists of ( coracoid, clavicle and scapula ) The coracoid is strong and articulate with the sternum The clavicles come together to form the furcula, or"wishbone". The scapula is a sabre-like lies on the dorsal side above the ribs pelvic girdle :- consists of two symmetrical halves, each half consists of three parts ( ilium, ischium and pubis ) pelvic girdle is fused with some vertebrae to form the the synsacrum

Fore-limbs (wings) :- consists of the same bones of reptiles and mammals ( humerus, radius and ulna which called radio-ulna ) but in a highly modified form Hind-limbs: consists of two bones ( femur, tibia and fibula which called tibio-fibula) ended by the hind foot which have 4 digits.