The Skeletal System

The skeleton is composed of bones, cartilages, joints, and ligaments. There are 206 bones in the human skeleton which are divided into the axial and appendicular divisions. The axial skeleton is comprised of the skull, vertebral column, and rib cage. The four appendages, the pectoral girdle and the pelvic girdle make up the appendicular skeleton.

The Facial Bones Include: 1. the nasal bones 2. the maxilla bones 3. the zygomatic bones 4. the mandible 5. the lacrimal bones 6. the palantine bones 7. the inferior conchae bones 8. the vomer bone

The Cranial Bones Include: 1. frontal bone 2. parietal bones (paired) 3. temporal bones (paired) 4. occipital bone 5. sphenoid bone 6. ethmoid bone

The vertebral column consists of 26 irregularly shaped bones. The vertebrae are divided into three types: cervical, thoracic, and lumbar.

The Vertebral Column

There are 7 cervical vertebrae. The first two, the atlas and axis, are specialized to articulate with the skull.

Cervical Vertebrae

C1 The Atlas

C2 The Axis

Thoracic Vertebrae

The cervical vertebrae are followed by 12 thoracic vertebrae. The thoracic vertebrae are specialized to articulate with the ribs.

The 5 lumbar vertebrae follow the thoracic vertebrae. These bones are more massive than the other vertebrae and help to support the weight of the body.

The Lumbar Vertebrae

The Sacrum and Coccyx

Inferior to the lumbar vertebrae is the sacrum, 5 fused vertebrae, and the coccyx or tailbone.

The sternum or breastbone includes the fusion of three bones: the manubrium, the body, and the xiphoid process.

The Sternum: 1. Jugular Notch 2. Manubrium 3. Sternal Angle 4. Body of Sternum 5. Xiphoid Process

Rib	There are 12 pairs of ribs. Seven pairs are true ribs which attach directly to the sternum. The remaining 5 pairs are false ribs attaching indirectly to the sternum. Pairs numbered 11 and 12 are called floating ribs because they lack an anterior attachment site.

The pectoral girdle is comprised of two bones: the clavicle and the scapula. The pectoral girdle serves to attach the upper limbs to the body.

The Pectoral Girdle: 1. Clavicle 2. Scapula 3. Humerus 4. Sternum 5. Cervical vertebrae 6. Thoracic vertebra

The Clavicle

The Scapula (lateral view): 1. Acromion process 2. Coracoid process 3. Glenoid cavity 4. Lateral (axillary) border 5. Spine

The brachial region of the upper limb consists of the humerus. The antebrachial (forearm) region has two bones, the radius and ulna. The hand is made up by the carpals, metacarpals, and phalanges.

The Humerus (anterior-proximal end): 1. Head of the humerus 2. Lesser tubercle 3. Intertubercular groove 4. Greater tubercle 5. Anatomical neck 6. Surgical neck

The Radius (right) and Ulna (left)(posterior view): 1. Posterior aspect of the olecranon process 2. Radial head 3. Neck of the radius 4. Radial Tuberosity 5. Styloid process of the radius 6. Styloid process of the ulna

The pelvic girdle attaches the lower limbs to the axial skeleton, protects the organs of the pelvis, and transmits the weight of the upper body to the lower limbs. The pelvic girdle is made of two hip bones also called os coxae or the coxal bone. The os coxae is comprised of three bones fused together: the ilium, the ischium, and the pubic bone.

The Pelvic Girdle: 1. Last lumbar vertebra (L5) 2. Sacrum 3. Coccyx 4. Pubic symphysis 5. Ischium 6. Pubis 7. Ilium 8. Obturator foramen 9. Femur

Key to the Os Coxae: 1. Anterior Superior Spine 2. Iliac Crest 3. Posterior Superior Spine 4. Posterior Inferior Spine 5. Greater Sciatic Notch 6. Body of Ilium 7. Ischial Spine 8. Lesser Sciatic Notch 9. Body of Ischium 10. Ischial Tuberosity 11. Obturator Foramen 12. Inferior Ramus of Ischium 13. Inferior Ramus of Pubis 14. Body of Pubis 15. Acetabulum 16. Anterior Inferior Spine

The tibia (red arrow), fibula and bones of the foot