Module 3 : Skeletal System

• The functions of the skull

  • To house and protect the brain
  • To house the special sense organs
  • To house and provide attachment for parts of the digestive system (teeth, tongue, etc.)
  • To provide attachment for the hyoid apparatus and the numerous muscles of mastication and facial expression
  • To provide a bony cavity through which air can enter the body
• Components of the Skull

  • Cranium
  • Nasal chambers
  • Mandible
  • Hyoid Apparatus
  • Skull Shapes
• Parietal bone


  • Forms much of the dorsal and lateral walls of the cranium
• Sphenoid bone


  • Unpaired bone, lying on the ventral aspect of the skull, forming the floor of the cranial cavity
• Frontal bone


  • Forms the front aspect of the cranium and contains an air-filled chambers called the frontal sinus
• Temporal bone


  • Lies below the parietal bone on the caudolateral surface of the skull
• Zygomatic bone (Jugal, Malar)

  • The zygomatic arch is an arch of bone that projects laterally from the skull, forming the cheekbone
• Occipital bone


  • Lies at the base of the skull on the caudal aspect
• Incisive bone (Premaxilla)


  • Most rostral bone of the skull and carries the incisor teeth
• Maxillary bone (Maxilla)


  • Forms the osseous lateral walls of the face and major part of the hard palate
• Nasal bone


  • Longitudinal bone forming the roof of the nasal cavity
• Lacrimal bone (Prefrontal)


  • Lies at the medial surface of the orbit, which houses the eye
• Pterygoid bone


  • Forms part of the lateral wall of the air passageway to the soft palate
• Palatine bone


  • Forms part of the hard palate, along with the maxilla and incisive bone
• Thyrohyoid


  • Articulate caudally with the rostral cornua of the thyroid cartilage of the larynx
• Epihyoid


  • Small, rounded bones situated between the stylohyoid and ceratohyoid; known as the ‘middle cornua’
• Stylohyoid


  • Articulate rostrally with the epihyoid and with the styloid process of the temporal bone caudally; it is the largest and often called the ‘great cornua’
• Basihyoid


  • The only unpaired bone and is considered as the base; it is short and flattened and lies in the transverse plane
• Ceratohyoid


  • Located in between the epihyoid and basihyoid; known as the ‘small cornua’
• Memory Aid: Sick Elephants Can Be Treated
• The head, particularly the nose, is long and narrow
• This is the ‘normal’ or average shape of the dog skull
• The cranium is often more rounded, and the nose is short and maybe pushed in, because of shortening of the nasal chambers, hard palate and mandible
• Functions of the Skeletal System

  • Support - It acts as an internal ‘scaffold’ upon which the body is built.
  • Locomotion - It provides attachment for muscles, which operate a system of levers (i.e., bones) to bring about movement.
  • Protection - It protects the underlying parts of the body.
  • Storage - It acts as a store for the essential minerals calcium and phosphate.
  • Haemopoiesis - Haemopoietic tissue forming the bone marrow manufactures the blood cells.
• Types of Bones


  • Long bones
  • Flat bones
  • Short bones
  • Irregular bones
• Special types of bones

  • Sesamoid bones
  • Pneumatic bones
  • Splanchnic bones
• Long Bones


  • Proportionally longer than they are wide.
  • Each has a central marrow cavity and a proximal and distal epiphysis.
  • Typical of the limb bones (femur, humerus).
  • Include bones of the metacarpus/metatarsus and phalanges.
• Short Bones


  • About as long as they are wide.
  • Have an outer layer of compact bone with a core of cancellous bone and no medullary cavity.
  • Examples of the short bones are carpals and tarsals.
• Flat Bones


  • Have two plates of compact bone with spongy bone in between. Forming a trabeculae crossing from one side of the bone to the other.
  • These bones have no marrow cavity but have small, irregular marrow spaces.
  • Examples of flat bones include pelvic bones, scapula and skull bones.
• Irregular Bones


  • Have a similar structure to short bones but are less uniform in shape.
  • They lie in the midline and are unpaired (e.g., vertebrae and some parts of the skull).
• Flat bones


  • Pelvic bones
  • Scapula
  • Skull bones
• Irregular Bones


  • Have similar structure to short bones but are less uniform in shape
  • Lie in the midline and are unpaired (e.g., vertebrae and some parts of the skull)
• Sesamoid Bones


  • Patella associated with the stifle joint
• Sesamoid Bones


  • Are sesame-seed-shaped bones that develop within a tendon that runs over an underlying prominence
  • Serve to change the angle at which the tendon passes over the bone and reduce 'wear and tear'
• Pneumatic Bones


  • Maxillary bones
  • Frontal bones
• Pneumatic Bones


  • Contain air-filled spaces known as 'sinuses' that reduce the weight of the bone
  • Highly present in avian species
• Splanchnic Bones


  • Os penis/baculum
• Splanchnic Bones


  • Bone that develops in a soft organ and is unattached to the rest of the skeleton
• Aberrant Long Bones


  • Ribs
• Parts of the Long Bones

  • A membrane lining the inner surface of the bony wall also identified as the lining membrane of the Bone marrow cavity
  • A fibrous membrane that covers the surface of a bone except where articular cartilage is located