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

The mammalian skeleton is split into the axial and appendicular skeletons The axial skeleton The skull :- is the skeleton of the head. It passes through three developmental stages ( membranocranium, chondro- cranium and osteocranium ). The skull is divided of two regions:- 1- neurocranium (cranium and sense capsules) 2- splancocranium (Jaws and hyoid apparatus )

The rest of the splanchnocranium has either disappeared or modified to form the laryngeal cartilages. Skull shape can differ significantly between different mammal species and eating habits play a large role in the structure of the skull for many mammals. The skull of human can be used to determine the sex because there are a number of differences between the male and female skulls. The chin, cranium, brow ridges and mandible are all larger in male skulls.

The vertebral column is divide into five regions ( cervical, thoracic, lumbar, sacral and caudal vertebrae. - Cervical Vertebrae : supports the neck and head and typically in mammals made up of 7 vertebrae. The first vertebra is called the 'Atlas' while the second is called the 'Axis'. - Thoracic Vertebrae : these are the bones from which the rib bones extend. These are usually 12-15 vertebrae.

- Lumbar Vertebrae : there are 4 or 7 lumbar vertebrae except in the toothed whales where there can be as many as 20 vertebrae - Sacral Vertebrae : There are usually 3-5 vertebrae. these bones support the pelvic girdle and are often fused together. - Caudal Vertebrae : The last region of the vertebral column is the caudal vertebrae. These small bones make up the tail. They are generally smaller and less complicated than the rest of the vertebrae.

The caudal vertebrae also do not contain the spinal column which ends at or before the sacral vertebrae, though they do contain some nerves and blood vessels. The number of the caudal vertebrae differ between mammal species while some mammals don't have tail. The sternum : or breastbone is actually made up of a number of smaller bones called 'sternebrae'. The front part of the sternum is keeled .

The appendicular skeleton The pectoral girdle :- consists of two pairs of bones, the large flat Scapula (shoulder bone) and the much smaller and more slender Clavicle (collar bone). In some mammals such as the Anisodactyla, Perissodactyla, Mysticeti and Odontoceti (Horses, Pigs, Deer, Buffaloes, etc. and Whales) the clavicle is absent. The scapula is the bone that the legs or arms start from, i.e. the humerus joins the far end of the scapula.

The pelvic girdle : consists of two halves, each of which made up of three bones fused together.( ilium, ischium and pubis ) The pelvis is also a useful bone in determining the sex of a human skeleton. The female pelvis in wider to accommodate childbirth and the shape of the pubis is much flatter. Fore-limbs (Arms) : is made up of three bones: the humerus, ulna and radius. The humerus fits into the pectoral girdle

The hand is made up from the carpel bones in the wrist, five metacarpals Hind-limbs (legs): consists of three long bones; The femur is the longest bone in the human body and is similar in length to the humerus in many four legged mammals. The tibia is the major bone of the lower leg and provides the majority of strength. The fibula runs down the outside of the tibia and extends lower than the tibia to connect to the side of the foot. In horses the fibula is partially fused with the tibia. The foot is very similar in structure to the hand.