Skeletal System
I. Ossification (os - bone, fic- to make)
Dependent on a proper supply of Ca and P to the bone tissue
II. Types of bones
a. Cortical bone (compact bone)- hard, dense, strong bone that forms the outer layer of a
bone.
b. Cancellous bone (spongy bone) - lighter, less strong bone that is found in the ends and
inner portions of long bones
III. Bone classification
a. long bones - bones with a shaft, two ends, and a marrow cavity (femor, radius)
b. short bones - cube-shaped bones with no marrow cavity (carpal, tarsal)
c. flat bones - thin flat bones ( pelvis)
d. pneumatic bones - sinus-containing bones (frontal bone)
e. irregular bones - umpaired bones (vertebrae)
f. sesamoid bones - small bones embedded in a tendon (patella)
IV. Bone formation
a. diaphysis - middle region of a long bone; composed of compact bone
b. epiphysis - end of the long bones; composed of cancellous bone
c. epiphyseal line (growth plate) - cartilage tissue that is constantly being replaced in long
bones
d. Periosteum -tough, fibrous tissue that forms the outer covering of the bone
e. Articular Surface - smooth layer of cartilage covering the epiphysis where one bone
forms a joint with another bone
f. Medullary cavity - space in the diaphysis that contains the marrow
g. Cortex - compact bone surrounding the medullary cavity.
h. Red marrow - forms blood; in older animals it is only found in the ends of the long
bones.
i. Yellow marrow - consists of adipose tissue.
V. Joints (Articulations)
A. Simple Joint - involving two bones
B. Compound Joint - involving more than 2 bones (Stifle)
C. Structural Classification
1. Fibrous joint (synarthroses) - united by fibrous tissue; allowing little or no
movement; these are often temporary joints
2. Cartilaginous joint (amphiarthroses) - united by fibrocartilage; slightly
moveable
3. Synovial joint (diarthroses- ball and socket joints) - united by synovial capsule;
freely moveable joint.
VI. Structural Support
a. Bone process - enlarged tissue where muscles and tendons attach
1. Bone head - rounded end of a bone
2. Tubercle -small, rounded surface for attachment of tends or muscles
3. Tuberosity - projecting part for attachment of tendons or muscles
4. Condyle - rounded projection that articulates with another bone
5. Crest - high projection or border projection
6. Process - projection
7. Protuberance - projecting part
8. Trochanter - broad, flat projection (femur)
b. Bone depression - openings or regions where one bone connects to another bone
1. Fossa - trench or hollow depressed area
2. Foramen - opening for blood vessels or nerves
3. Fissure - narrow, deep, slit-like opening
4. Sinus - cavity within a bone
VII. Skull
a. frontal - forms the roof of the cranial cavity; where the horn processes come from
b. parietal - paired bones that form the roof the caudal cavity.
c. Occipital condyles- forms the caudal aspect of the cranial cavity; opening for the spinal
cord
d. Temporal - paired bones that form the sides and base of the cranium
e. Zygomatic arch - cheekbone
f. maxilla - upper jaw
g. mandible - lower jaw
h. lacrimal fossa - tear duct
i. mental foramen j. orbit - socket for the eye
k. external acoustic meatus l. paracondylar process m. mastoid process n. nuchal crest o. tympanic bulla p. coronoid process -
Skull Shapes:
1. Brachycephalic - short, wide heads with the “smashed in” face
2. Dolichocephalic - dogs have narrow, long heads
3. Mesocephalic - dogs have average width to their head
VIII. Vertebrae (spondyl)
a. Cervical - neck
1. Atlas (C1)
2. Axis (C2)
b. Thoracic
c. Lumbar
d. Sacrum
e. Coccygeal
f. intervertebral disc - cartilage disc that cushions each vertebrae
IX. Ribs (costal)
a. sternum - breastbone
b. xiphoid process - caudal portion of the sternum
c. clavicle (collarbone) - pigs, ruminants and horses do not have clavicles
X. Front Limb
a. Scapula - shoulder blade
b. Spine of the scapula
c. Humerus
d. Radius
e. Ulna
f. Olecranon - elbow
g. Carpals - wrist
h. Metacarpals
i. Phalanges - fingers/toes
j. Sesamoid - small nodular bones embedded in a tendon or joint capsule
k. Cannon (III metacarpal)
l. Splint
m. Long Pastern (P1)
n. Short Pastern (P2)
o. Coffin bone (P3)
p. Navicular
XI. Hind limb
a. femur
b. tibia
c. fibula
d. patella - knee
e. Tarsal - ankle
f. Metatarsal - foot
g. Phalange - toes
h. Sesamoid - small nodular bones embedded in a tendon or joint capsule
i. Cannon (III metacarpal)
j. Splint
k. Long Pastern (P1)
l. Short Pastern (P2)
m. Coffin bone (P3)
n. Navicular
XII. Pelvis
a. Ilium
b. Acetabulum (hip joint)
c. Ischium
d. Pubis
e. Pelvic symphysis
f. Obturator foramen
XIII. Vocabulary
a. oste(o) - bone
1. Oste/itis - inflammation of the bone
2. Osteo/dystrophy - inadequate formation of bone tissue
3. Osteo/genesis - formation of bone tissue
4. Osteo/myel/itis - inflammation of the bone and bone marrow. May result in
bone destruction if it spreads to the joints.
b. chondr(o) - cartilage
1. Chondro/malacia - softening of the cartilage
2. Chondro/placia - formation of cartilage
c. Orth - straight
d. Physis - to grow
e. Porosis - passage
1. Osteo/porosis - bone breaking down by forming holes. Bones become weak
due to loss of Ca.
f. bursa - capsule around the joint containing fluid
1. Burs/itis - inflammation of the bursa sac
g. reduction - restoration of a fractured bone to its normal place or position
h. arthritis - inflammation of the joints
i. Dislocation -displacement of a bone from its joint
j. Sprain - injury to ligaments; twisting of the joint with partial rupture of its ligaments.
XIV. Pathological Conditions
a. Osteogenic Sarcoma - malignant tumor from the bone. Common in dogs and cats but
rare in other species. Large breeds more frequently affected. Lameness and swelling of
the bone with rapid metastasis to the lungs.
b. Fracture
a. Closed (Simple) - bone broken but does not create an open wound
b. Compound (open) - broken bone with open wound created by the bone sticking
out. Complicated with infections
c. Comminuted - bone splintered or crushed. Common with gunshot wounds
d. Greenstick - bone is partially fx
e. Compression - broken bone produced when the bones are pressed together
f. Spiral - broken bone in which the bone is twisted apart or spiraled apart
g. Avulsion - broken bone in which the site of muscle, tendon, ligament insertion
is detached by a forceful pull
h. Chip - caused by overextension at speed in horse
i. Slab - surface pieces are broken off. Seen in carpal bones
c. Ankylosing Spondylitis - progressive arthritis with stiffening joints in the vertebrae.
(Ankylo - bent; spondylitis - vertebrae)
d. Navicular Disease - lameness in horses caused by the navicular bone turning or the
sesamoid bone going over the bone
e. Ring bone - periosteal bone deposition on the phalanges. Occurring near the pastern
or coffin joint
f. Hip Dysplacia - Lameness ; Mostly in large dogs. Common causes in dogs are
1. Genetic
2. Nutrition
3. Fat baby
g. Splint - inflammation of the horse’s interossesous ligaments and build-up of bone
between the splint and cannon bones
h. OCD(osteochondrosis dissecans) - 2nd most common hock problem; Fast growing
cartilage .
i. Wobbler Syndrome - stenosis (narrowing) of cervical vertebrae. Common in Bassets,
Borzois, Dobies, Great Danes, Throughbreds. Clinical signs develop slowly with
weakness, ataxia.
j. Intervertebral Disk Disease - one or more intervertebral disc dengenerates. This
usually is disk material being squeezed out and puts pressure on the spinal chord. Signs
include pain, numbness, weakness, paralysis. Common in Dachshunds at the cervical
junction. Treatment includes surgery and cage rest.