Veterinary Gross Anatomy

VERTEBRAL COLUMN

• Certain vertebrae remain free throughout life and are termed movable or true vertebrae and certain others get used together with the adjacent ones and are termed fixed or false vertebrae.
• The column as a whole may be divided for description into five regions - cervical, thoracic, lumbar, sacral and coccygeal accordingly as they form the skeleton of the neck, back, loins, croup and tail respectively.
• The number of bones in each region except the last is fairly constant in each species so that their number can be expressed as a formula called the vertebral formula.
• The vertebral formula in domestic animals is given below.

	Cervical vertebrae	Thoracic vertebrae	Lumbar vertebrae	Sacral vertebrae	Coccygeal vertebrae
Ox	C-7	T-13	L-6	S-5	Cy-18-20
Sheep	C-7	T-13	L-6-7	S-4	Cy-16-18
Horse	C-7	T-18	L-6	S-4	Cy-15-21
Pig	C-7	T-14-15	L-6-7	S-4	Cy-20-23
Dog	C-7	T-13	L-3	S-3	Cy-20-23
Rabbit	C-7	T-12	L-4	S-4	Cy-16
Fowl	C-13-14	T-7	LS-14	-	Cy-7

VERTEBRAE

• All the bones of the column which are constructed on the same general plan are termed typical vertebrae.Those that deviate from the general plan are atypical vertebra.
• The typical vertebrae presents a body, an arch and processes.

Body

• It is the fundamental part of the vertebra around which the other parts are grouped.
• It is in the form of a solid rod.
• The anterior end is convex and the posterior end is correspondingly concave.
• The anterior end of one vertebra meets the posterior end of the preceding vertebra and between them is interposed a disc of fibrocartilage -the intervertebral disc.
• The dorsal surface of the body is flat and forms the floor of the vertebral foramen while the ventral face presents centrally the ventral spinous process for muscular and ligamentous attachments.

Neural arch

• The neural arch is situated on the superior face of the body and it forms with the body, a bony ring - the vertebral foramen.
• The entire series of these rings constitutes a canal called the spinal or vertebral canal for the lodgment of the spinal cord.
• Each half of the arch is made up of a vertical pedicle and a horizontal lamina.
• The anterior and posterior edges of the pedicles exhibit notches - the vertebral notches which when adjacent vertebrae are in position circumscribe the intervertebral foramina for the passage of vessels and spinal nerves.

Processes

• The processes of the vertebra are variable in size, development and shape in the different regions. They are:
• Articular or Oblique Processes: These are four in number two of which are placed on the anterior and two on the posterior edge arch. These present articular area, which face upward in the anterior and downward in the posterior processes. The anterior processes of one vertebra are overlapped by and articulate with the posterior processes of vertebra in front and form synovial joints. The non-articular area serves for muscular and ligamentous attachments.
• Transverse Processes : They are two in number for each vertebra, one on either side spring from the lateral aspect of the body or the lower part of the arch. These vary in size and shape in the different regions.
• Spinous Processes (neural or superior spines): They are single, projecting from the middle of the dorsal part of the neural arch. They vary greatly in size, form and direction in different vertebrae.
• Ventral spinous processes: These are also single and are situated on the ventral aspect of the bodies of the vertebrae.
• Mamillary processes: are those situated between the transverse and anterior articular processes or on the latter. e.g. lumbar vertebrae.
• Accessory processes: are situated between the transverse and posterior articular processes. e.g. lumbar vertebrae of dog.