MODULE 3 & 4 :Arthrology and Ligaments

• Functions of Skeletal System

  1. Support: Acts as an internal 'scaffold' upon which the body is built

  2. Locomotion: Provides attachment for muscles, which operate a system of levers (i.e. bones) to bring about movement

  3. Protection: Protects the underlying parts of the body

  4. Storage: Acts as a store for the essential mineral calcium and phosphate

  5. Haemopoiesis: Haemopoietic tissue forming the bone marrow manufactures the blood cells
• Types of Bones

  • Long bones
  • Short bones
  • Flat bones
  • Irregular 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 (do not have evident marrow cavity unlike femur and humerus)
• 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 (no marrow cavity)
  • Examples are the carpals on the fore paw and tarsals on the hind paw
• Flat bones


  • Have two plates of compact bone with spongy bone in between, forming trabeculae crossing from one side of the bone to the other
  • These bones have no marrow cavity but have small irregular marrow spaces
  • Examples include pelvic cavity, 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)
• Special Types of Bones

  • Sesamoid Bones
  • Pneumatic Bones
  • Splanchnic Bones
  • Aberrant Long Bones
• 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'
  • Example: Patella associated with a stifle joint
• Pneumatic Bones


  • Contain air-filled spaces known as 'sinuses' that reduce the weight of the bone
  • Examples include Maxillary and Frontal bones
• Splanchnic Bones


  • Bones that develop in a soft organ and are unattached to the rest of the skeleton
  • Example: Os penis/baculum
• Aberrant Long Bones


  • Ribs
• Long Bones

  • Compact bone: Dense or cortical bone, the hard layer that constitutes the exterior of most bones and forms almost the entire shaft of the long bone
  • Cancellous (spongy) bone: Enclosed by the compact bone
• Bones

  • Ribs
  • Cervical vertebrae
  • Thoracic vertebrae
  • Lumbar vertebrae
  • Few sacral vertebrae
  • Sternum
  • Aberrant long bones
• Long Bones

  • Compact bone: Dense or cortical bone, the hard layer that constitutes the exterior of most bones and forms almost the entire shaft of the long bone
  • Cancellous (spongy) bone: Enclosed by the compact bone
• Spongy bones

  • Categorized by loosely arranged bony plates or spicules known as trabeculae (aligned according to the mechanical stress that the bones are experiencing)
  • The cavities between the plates are occupied by marrow spaces
• Medullary Cavity

  1. Hollow shaft of long bones

  2. Contains the marrow

  3. In young animals, there is red marrow. When it ages, this is occupied by yellow marrow or adipose tissue
• Articular Cartilage


  • Thin layer of hyaline cartilage that covers the articular surface
  • Articular surfaces are structures that attach to a cavity/fossa in the other bones and thus form a joint
• Nutrient arteries


  Passes through the nutrient foramen to the medullary cavity where it divides and sends branches through the marrow openings
• Epiphysis


  Refers to the endline of a long bone
• Proximal Epiphysis


  The end closer to the body
• Distal Epiphysis


  The end far from the body
• Diaphysis


  Body of the long bone between the epiphysis
• Metaphysis

  In mature bone, flared are adjacent to the epiphysis. Region between diaphysis and epiphysis
• Epiphyseal cartilage


  A layer of hyaline cartilage within the metaphysis of an immature bone which separates the diaphysis from the epiphysis
• As we get older, the epiphyseal cartilage closes, that’s why our height doesn’t increase anymore
• The Canine Skeleton

  • Axial
  • Appendicular
  • Splanchnic
• Axial Skeleton runs from the skull to the tip of the tail and includes the skull, mandible, vertebrae, and sternum
• Appendicular Skeleton consists of the pectoral (front) and pelvic (hind) limbs and the shoulder and pelvic girdles that attach (or append) them to the body
• Splanchnic consists of the os penis of the dog
• Average count of bones in the Canine Skeleton: Skull and hyoid - 50, Vertebral column - 50, Ribs and sternum - 34, Thoracic Limb - 90, Pelvic limb - 96, Splanchnic Bone (Os penis) - 1, Total - 321
• Skull

  • To house and protect the brain
  • To house the special sense organs (eyes, mouth)
  • 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
• Sutures


  Firm and immovable joints that allow for expansion of the skull in growing animals
• Cranium


  • The caudal part of the skull that forms the bony case in which the brain sits
  • Tympanic bulla - the structure that houses the middle ear
  • External acoustic meatus - opening to the tympanic bulla closed by the tympanic membrane or ear drum
  • Zygomatic process of the frontal bone
  • Nuchal crest - transition from the dorsal to the caudal bone
  • Sphenoid bone - area that houses the perpetuary glands via a depression called sella turcica
• Mandibular symphysis fractures


  The most common type of mandibular fracture in cats. Can be treated with a cerclage wire placed around the two sides of the lower jaw to align the bones
• Mandible

  • Ramus - vertical part with no teeth attached to the zygomatic arch
  • Body - horizontal part bearing the lower incisor teeth, canine teeth, premolar teeth, and the molar teeth
• Structures in Mandible

  • Mental foramina
  • Mandibular foramen
  • Masseteric fossa
  • Coronoid process
• Mandible structures

  • Rostral opening in the mandibular canal
  • Mandibular foramen
  • Masseteric fossa
  • Coronoid process
  • Condyloid process
  • Mandibular notch
• Hyoid apparatus components

  • Present in the intermandibular space and consists of a number of bones and cartilages
  • Attached to the styloid process of each temporal bone
• Skull shapes in dogs

  • Brachycephalic - bulldogs, Pekingese, boxers, pug
  • Mesaticephalic - Beagles, Golden Retrievers, Labrador Retrievers, German Shepherds, Pomeranians
  • Dolichocephalic - Greyhounds, Collies, Setters, Dachshunds, Italian Greyhounds, Great Danes
• 3D tomography breeds

  • 1 - german shepherd
  • 2 - boxer
  • 3 - bulldog
  • 4 - French bulldog
  • 5 - boston terrier
  • 6 - pug