Anatomy I - Axial Skeleton

Axial Skeleton

Bones found on or near the medial plane (skull, hyoid bone, vertebral column, ribs & sternum. 

Vertebral Regions

“C” - Cervical (neck), “T” -Throracic (chest), “L” - Lumbar (back), “S” - Sacral (hind end), “CY” - Coccygeal (continuation of tail). 

Vertebral Formula Dog

C7, T13, L7, S3, CY 20-23

Vertebral Formulas CATS

C7, T13, L7, S3, CY 5-23

Vertebral Formulas HUMANS

C7, T12, L5, S5, CY 4

Components Of A Typical Vertebra : Body / Arch

cylinder on the front side / roof, sides of spinal cord

Processes

Spinous (dorsal/up), Ventral (down), Transverse (side to side), Cranial (towards head), Caudal (toward hindend)

C1(ATLAS)

Large transverse processes (wings), large vertebra but small body, concave articular surfaces, connects to the skull,  hing joint (yes/no movement).

C2 (AXIS)

Allows head to rotate (no motion), has a pivot joint, large vertebra, prominent dorsal spinal process.

C2 Joint Surface

Is rounded at the top and hollowed at the bottom

Dens

Cranial extension in the body of C2 (fits into postier of Atlas), forms pivot joint (rotate head).

C3- C7

Size decreases, height increases towards C7. Rudimentary ventral spinous processes. Large, plate-like transverse processes project caudolaterally. C7 has facets that articulate with the head of the first ribs. Foramina lateral to the body carry nerves and blood vessels.

Thoracic

Rib attachments, normal size body, most is made up of tall dorsal spinal processes. 

Lumbar

Long transverse processes, short to moderate dorsal spinous processes, (hugging vertebra in front). 

Sacral  

Fused vertebrae, cranially last lumber, caudally first coccygeal vertebra, craniolaterally wings of pelvis.

Coccygeal

Look similar to sacral and lumbar, decrease in size with less processes and more cylindrical shape moving caudally. 

Ligamentum Nuchae

Attaches between C2 and T1, helps to support the head and neck.

Rib Structure

Head connects to the spine, the neck is the short section after it, and the tubercle joins with the vertebra. The angle is where the rib curves, and the shaft is the long main part with the costal groove on the underside for blood vessels and nerves. The sternal end connects to the breastbone.

Sternal (True Ribs)

Extend directly & continuously from vertebrae to attach by the costal cartilage to the sternum

Asternal (False Ribs)

Dont attach directly to the sternum, connect to the costal cartilage of the rib cranial to it.

Floating Ribs

No connection to sternum at any point. 

Intercostal Spaces

Area between each rib, contains skeletal muscle, surgery entry point for thoracic surgery, allows for flexibility in the chest. 

Manubrium Sterni

Cranial end of the sternum, projects cranial to the 1st pair of ribs (so does carinform cartilage). 

Sternum Body

Formed from union of segments known as sternabrae (youth, separated / adult, fused).

Xiphoid Process

Caudal extremity of sternum, xiphoid cartilage projects caudally. 

Functions Of The Sternum

Form floor of the bony thorax, attachment to coastal cartilages of sternal ribs, place of origin for pectoral muscles (protection, flexibility in chest expansion, pulling in of forelimbs.)

Horse sternum

Long, boat-shaped with a prominent sternal keel (ridge/crest)

Cow Sternum

Wider and flatter

Pig Sternum

Long wide and flattened

Dog Sternum

Slender made of eight segments

Cat Sternum

Narrow & elongated with eight segments