The Skeletal System
The Skeletal System
Cancellous Bone-the lightweight, porous inner layer of bones
Compact Bone-the dense, hard outer layer of all bones
Long Bones-a bone that is significantly longer than it is wide
Most of the bones of the limbs are long bones
Each long bone has a proximal epiphysis and a distal epiphysis
The diaphysis is composed primarily of compact bone
Between the epiphyses and diaphysis, there are the areas where the bone grows longer in young animals
Once an animal reaches its full size, the epiphyseal plates are replaced by solid bone through a process called ossification
Short Bones-roughly cube-shaped, with its length, width, and thickness being approximately equal
Carpal and tarsal bones are the most common short bones in the body
Flat Bones0mostly flat and thin
The pelvis bones and the scapula are prominent flat bones as are some of the skull bones
Irregular Bones-odd shaped and don’t fit into any of the other three categores
Articular Surfaces-smooth areas of compact bone that come in contact with smooth surfaces of other bone to form a joint
The articular surfaces are covered with hyaline cartilage
Condyle-a large, round articular surface
The distal ends of the femur and humerus, and the occipital bone have the most prominent condyles
Head-found at the proximal end of a long bone
It is mostly spherical in shape
The head is usually joined to the rest of the bone by a narrowed region called the neck
Facet-a flat articular surface
It is found on carpal bones, tarsal bones, vertebrae, and some long bones, such as the radius and ulna
Processes-the lumps and bumps on bones
Condyles and heads on long bones are considered processes, but they have a specific articular function, so they are classified as articular surfaces
Most of the other processes on bones are plaes where the tendons of muscles attach to the bone
Larger processes are where more powerful muscles attach
Some of the names used are trochanter, tubercle, tuber, crest, olecranon, spine, and wing
Foramen-a hole in a bone
Usually, it is a passageway for blood vessels to nerves to enter and leave the bone
Fossa-a depressed, sunken area on the surface of a bone
Bone fossae are usually occupied by muscles or tendons
The Skeleton
Even though an animal has only one complete skeleton, we are going to divide it into two main parts for the purpose of studying bones
Axial Skeleton-made up of the bones located on or near the central cranial-caudal axil of the body, the skull, hyoid bone, spinal column, ribs, and sternum
Appendicular Skeleton-made up of the main appendages of the body: the thoracic limbs and the pelvic limbs
The axial skeleton is made up of the skull hyoid bone, spinal column, ribs, and sternum
All the bones of the axial skeleton are located at or near the median plane of the animal’s body
Skull-the most complex part of the skeleton
It is made up of bones that, with one exception, are united by jagged immovable fibrous joints call sutures
The only freely movable joint is the between the mandible and the temporal bone, called the temporomandibular joint or TMJ
The bones of the skull can be conveniently grouped into the bones of the cranium which surround the brain, and the bones of the face
The only internal bones we will cover are the nasal tubinates, which play important roles in the conditioning of inhaled air on its way to the lungs
Occipital bone-single bone that forms the base of the skull
Foramen Magnum-the large opening where the spinal cord exits the skull
Occipital Condyles-form a joint with the atlas
Interparietal Bones-two small bones on the dorsal midline between the occipital bone and the parietal bones
Parietal Bones-two bones that form the dorsolateral portion of the cranium
Temporal Bones-two bones that form the ventrolateral portion of the cranium
External Acoustic Meatus-Opening that leads to the middle and inner ear cavities
Tympanic Bullae-egg-shaped swellings on the ventral surface, contain the middle ear structures
Frontal Bones-two bones that form the forehead part of the skull
Cornual Process-the bony, cone-shaped projection of the frontal bone that serves as the internal core of the horn in ruminants like cattle, sheep, and goats
Incisive Bones-two bones that are the most rostral skull bones
Nasal Bones-two bones that form the bridge of the nose, the dorsal part of the nasal cavity
Maxillary Bones-two bones that make up most of the upper jaw
Lacrimal Bones-two small bones that form part of the orbit of the eye
Zygomatic Bones-two bones that form a portion of the orbit of the eye and a portion of the zygomatic arc
Mandible-two bones united rostrally by the mandibular symphysis in dogs, cats, and cattle
Shaft-the horizontal part that houses all the lower teeth
Ramus-the vertical part at the caudal end that forms the temporomandibular joint with the temporal bone
Turbinate-thin scroll-like bones that fill most of the space in the nasal cavities
The hyoid bone attaches to the temporal bones and supports the base of the tongue, the pharynx, and the larynx
It consists of several individual parts united by cartilage but is usually referred to as a single bone
Vertebrae-a series of irregular bones that extend from the skull to the tip of the tail
Body-the large, drum-shaped anterior portion of the vertebra
Arch-the bony ring that attaches to the posterior side of the vertebral body
Processes-bony projections that extend from the vertebral arch
Spinous Process- projects posteriorly and inferiorly from the junction of the two laminae
Transverse Processes-project laterally from the junction of the pedicle and lamina on each side
Articular Processes-two superior and two inferior projections that form joints with neighboring vertebrae
Cervical-neck region
Thoracic-chest region
Lumbar-abdominal region
Sacral-pelvis region
Coccygeal-tail region
Most vertebrae do not have specific names but are identified by numbers within each region from cranial to caudal
A shorthand method of identifying vertebrae uses the abbreviation for the vertebral group followed by the number of the particular vertebra
For example, vertebra C5 is the fifth cervical vertebra and T10 is the tenth thoracic vertebra
The first two cervical vertebrae are unusual in shape compared with the rest of the vertebrae and they have specific names
Atlas-the first cervical vertebra
It does not have a vertebral body but consists of a bony ring that the spinal cord passes through, and two large transverse processes called the wings of the atlas
Axis-the second cervical vertebra
Its main characteristics are a large, bladelike spinous process and the peglike dens on its cranial end that tucks into the caudal end of the atlas to help form and stabilize the atlantoaxial joint
The rest of the cervical vertebrae are fairly normal in appearance and are just identified by number, like the rest of the vertebrae
The number of thoracic vertebrae is usually equal to the numbers f pairs of ribs the animal has
The main characteristics of thoracic vertebrae are their tall spinous processes and their lateral articular facets, which form joints with the heads of the ribs
The lumbar vertebrae are the most massive-looking vertebrae of the spinal column
They have to support the weight of the abdominal organs without the aid of the ribs, which help support the organs in the chest
The sacral vertebrae are fused into a single solid structure called the sacrum
The sacrum forms a joint with the ilium of the pelvis, the sacroiliac joint
The coccygeal vertebrae are the bones of the tail
At the cranial end, the first few coccygeal vertebrae look like small versions of normal vertebrae
Further caudally, they gradually turn into simple little rods of bone
Ribs are flat bones that form the lateral sides of the thorax
Costal Cartilage-bars of hyaline cartilage that extend from the anterior ends of the ribs
Costochondral Junction-the specific point where the bony part of a rib meets its costal cartilage
The costal cartilages join either the sternum or the costal cartilage of the ribs ahead of them
Sternum-breastbone, made up of bones called sternebrae
Manubrium-the first sternabrae
Xiphoid-the last sternabrae
A piece of cartilage that extends off the caudal end of the xiphoid process is the xiphoid cartilage, which can be palpated at the caudal end of the sternum in most animals
The appendicular skeleton is made up of the thoracic and pelvic limb bones of the animal
They make up the main appendages of the body, hence the name
Thoracic Limb-the front leg
In most domestic animals, it has no bony connection to the axial skeleton
Instead, the weight of the front part of the body is supported by a sluglike arrangement of muscles and tendons
Scapula-a flat, triangular bone located on the back of the thoracic cage
Spine-ridge that projects laterally
Glenoid Cavity-the socket part of the ball-and-socket shoulder joint
Neck-joins the glenoid cavity to the main part of the bone
Humerus-the longest and largest bone of the upper limb, extending from the shoulder to the elbow
Head-the ball part of the ball and socket shoulder joint
Neck-joins the head to the shaft
Greater Tubercle-a large process to which shoulder muscles attach
Condyle-the distal articular surface
Epicondyles-the knobs on the medial and lateral sides of the condyle
Olecranon Fossa-the indentation on the caudal surface just proximal to the condyle, which the anconeal process of the ulna tucks into when the elbow is extended
Ulna-long bone of the antebrachium
Olecranon Process-the attachment site for the triceps brachii muscle
Trochlear Notch-a half-moon-shaped, concave articular surface that wraps around the trochlea of the humeral condyle to help make the elbow joint a very tight and secure joint
Anconeal process-a beak shaped process at the proximal end of the trochlear notch
Coronoid Processes-located on the ends of the horizontal concave radial notch
Radial Notch-where the proximal end of the radius articulates with the ulna
Styloid Process-articulates with the carpus
Radius-main weight-bearing bone of the antebrachium
Head-has a large, concave articular surface that articulates with the capitulum of the humeral condyle to form part of the elbow joint
Neck-connects the head with the shaft of the bone
Styloid Process-articulates with the carpus
Carpal Bones/Carpus-located immediately distal to the radius and ulna
Accessory Carpal-protrudes backwards on the lateral side of the carpus
Metacarpal Bones-extend distally from distal row of carpal bones to the proximal phalanges of the digit
Cannon Bone-large metacarpal bone formed from two fused bones-metacarpals III and IV
Splint Bones-metacarpals II and IV
Phalanges-the individual bones that make up the digits
Proximal Sesamoid Bones-located on the palmar surface of the joint between the metacarpal and the proximal phalanx
Distal Sesamoid Bone-located on the palmar surface of the joint between the middle and distal phalanges
Pelvic Limb-the hind leg
From proximal to distal, the bones of the pelvic limb are the pelvis, femur, tibia and fibular, tarsal bones, metatarsal bones, and phalanges
Pelvis-develops from three separate bones on each side that eventually fuse into a solid structure
Ilium-the cranial most area of the pelvis
Ischium-the caudal most area of the pelvis
Pubis-located medially and forms the cranial part of the pelvic floor
Acetabulum-receives the head of the femur to form he hip joint
Obturator Foramina-two large holes on either side of the pelvic symphysis that serve to reduce the weight of the pelvis
Femur-long bone of the thigh
Head-the ball part of the ball and socket hip joint
Neck-joins the head to the shaft
Greater Trochanter-the large process to which the gluteal muscles attach
Condyles-the distal articular surfaces
Epicondyles-the knobs on the medial and lateral sides of the condyles
Patella-kneecap
Fabellae-two small sesamoid bones in the proximal gastrocnemius muscle tendons of dogs and cats
Tibia-Main weight bearing bone of the lower leg
Condyles-articulate with the condyles of the femur
Tibial crest-a ridge of bone that continues distally from the tibial tuberosity
Tibial Tuberosity-the prominent, bony bump on the anterior (surface of the tibia, located just below the knee join
Medial Malleolus-a medially facing rounded process on the distal end of the tibia
Fibula-thin but complete bone in dog and cat
Lateral Malleolus-the laterally facing rounded process on the distal end of the fibula
Tarsal Bones-located immediately distal to the tibia and fibula
Calcaneus-projects upward and backward to form the point of the hock
Metatarsal Bones-similar to metacarpal bones
Cannon Bone-a large metatarsal bone formed from two fused bones-metatarsals III and IV
Splint Bones-Metatarsals II and IV
Phalanges-similar to the phalanges of the thoracic limbs
Proximal Sesamoid Bones-located on the plantar surface of the joint between the metatarsal and the proximal phalanx
Distal Sesamoid Bone-located on the plantar surface of the joint between the middle and distal phalanges
Joints-where bones connect with each other
Fibrous Joints-also known as synarthroses, bones are firmly united by fibrous tissue
ex. Skull bones
Cartilaginous Joints-also known as amphiarthroses, bones are united by fibrocartilage
ex. Pelvic symphysis, Mandibular symphysis
Synovial Joints-also known as diarthroses, allow free movement
Types
Hinge Joint-elbow, joints of digits
Gliding Joint-carpus
Pivot Joint-atlantoaxial joint
Ball and Socket Joint-shoulder, hip
Movements
Flexion-decreased angle between the bones
Extension-increased angle between bones
Adduction-movement of an extremity toward the median plane
Abduction-movement of an extremity away from the median plane
Rotation-twisting movement
Circumduction-movement of an extremity so the distal end moves in a circle