Anatomical terms in dogs

Above is a diagram showing the commonly used directional terms and planes in veterinary medicine.

Dorsal structures (or positions) lie toward the back (dorsum) of the trunk or by extension, toward the corresponding surface of the head or tail.

Ventral structures lie toward the belly (venter) or the corresponding surface of the head or tail.

Cranial structures lie toward the head (cranium, skull), caudal ones toward the tail (cauda).

Within the  head, structures toward the muzzle (rostrum)  are said to be rostral; caudal remains appropriate.

Medial structures lie toward the median plane (medianus, in the middle) that divides the body into symmetrical right and left “halves”.

Lateral structures lie toward the side (latus, flank) of the animal.

Different conventions apply within the limbs. Structures that lie toward the junction with the body are
 proximal (proximus, near), whereas those at a greater distance are distal (distantia, distance).

Within the proximal part of the limb, structures that lie toward the “front” are said to be cranial, those that lie toward the “rear” caudal.

Within the remaining distal part of the  limb, structures toward the “front” are dorsal (dorsum, back  of  the  hand) and those toward the “rear” are palmar (palma, palm of the hand) in the forelimb or plantar (planta, sole of the foot) in the hind limb.

The median plane divides the body into symmetrical right and left halves.
Any plane parallel to this is a sagittal plane and those close to the median are sometimes termed paramedian planes.

A dorsal plane sections the trunk or other part parallel to the dorsal surface.

A transverse plane transects the trunk, head, limb or other appendage perpendicular to its own long axis.

HEAD INJURIES IN HORSES - Diagnosis and treatment

Head injuries can result in severe CNS (Central Nervous System) damage.

An injury can be divided into:

1). Primary (contusion, lacerations, or hemorrhage causing acute damage);
2). Secondary (subsequent edema, reperfusion injury, and necrosis).

Causes of head injury in horses include:  

1. Direct trauma from a fall;
2. Blows to the head.

   The associated injuries include basisphenoid fractures and avulsion of ventral straight muscles of the head. Basisphenoid fractures can result in acute optic nerve damage and cerebral signs. Temporary or permanent blindness may result.


1. Radiography; 
2. CT

 Treatment is supportive care and is focused on minimizing secondary brain damage.

  Head injury therapy is designed to minimize secondary CNS damage. 
  Horses with head injury can be severely ataxic and should be handled and moved with extreme caution.

1. If the horse is down, short-term general anesthesia is best used while moving.
2. If hypoventilation develops, the horse should be intubated and ventilation assisted to prevent hyper-capnea.
3. NSAIDs (Non-Steroidal Anti-Inflammatory drugs) are used to minimize inflammation.
4. Although controversial, corticosteroids may be indicated if used in the immediate phase of injury.
5. Dimethyl sulfoxide (DMSO) is often used to minimize secondary edema.
6. Magnesium has recently been proposed as another therapeutic agent for acute head injury.
7. Wound management( debridement, suture)
8. Fracture treatment

Skeleton and classes of bones in animals

The term skeleton is applied to the framework of hard structures which supports and protects the soft tissues of animals. In the descriptive anatomy of the higher animals it is usually restricted to the bones and cartilages, although the ligaments which bind these together might well be included.

In zoology the term is used in a much more comprehensive sense and includes all the harder supporting and protecting structures.
When the latter are situated externally, they form an exoskeleton, derived from the ectoderm. e.g. the shells and chitinous coverings of many invertebrates, the scales of fishes, the shields of turtles and the feathers, hair and hoofs of the higher vertebrates.
The endoskeleton is embedded in the soft tissues. It is derived chiefly from the mesoderm, but includes the notochord or primitive axial skeleton, which is of entodermal origin.

The skeleton may be divided primarily into three parts:
(1) axial,
(2) appendicular,
(3) splanchnic.

The axial skeleton comprises the vertebral column, ribs, sternum, and skull.
The appendicular skeleton includes the bones of the limbs.
The splanchnic skeleton consists of certain bones developed in the substance of some of the viscera or soft organs, e.g. the os penis of the dog and the os cordis of the ox.

The number of the bones of the skeleton of an animal varies with age, owing to the fusion during growth of skeletal elements which are separate in the foetus or the young subject. Even in adults of the same species numerical variations occur, e. g., the tarsus of the horse may consist of six or seven bones, and the carpus
of seven or eight. In all the domestic mammals the number of coccygeal vertebrae varies considerably.

The bones are commonly divided into four classes according to their shape and function:
(1) Long bones (Ossa longa) are typically of elongated cylindrical form with enlarged extremities. They occur in the limbs, where they act as supporting columns and as levers. The cylindrical part, termed the shaft or body (Corpus), is tubular and incloses the medullary cavity, which contains the medulla or marrow.
(2) Flat bones (Ossa plana) are expanded in two directions. They furnish sufficient area for the attachment of muscles and afford protection to the organs which they cover.
(3) Short bones (Ossa brevia), such as those of the carpus and tarsus, present somewhat similar dimensions in length, breadth, and thickness. Their chief function appears to be that of diffusing concussion. Sesamoid bones, which are developed in the capsules of some joints or in tendons, may be included in this group. They diminish friction or change the direction of tendons.
(4) Irregular bones. This group would include bones of irregular shape, such as the vertebrae and the bones of the cranial base. They are median and unpaired. Their functions are various and not so clearly specialized as those of the preceding classes.

This classification is not entirely satisfactory; some bones, e. g., the ribs are not clearly provided for and others might be variously placed.

Hairs in animals - Structure/ parts/ types/ tactile hairs

In animals hairs cover nearly the entire body surface, except the 
1) planum nasale, 
2) anus, 
3) vulvar lips and 
4) limb pads. 

Hairs are cornified filiform structures that are formed by the skin. The hair is subdivided into
1) the shaft which projects beyond the surface of the skin,
2) the root which is obliquely oriented within the dermis and 
3) the hair bulb, the proximal expanded part. 
Hair root and hair bulb are in a divided epithelial root sheath (Vagina epithelialis radicularis). The outer part of the sheath is continuous with the superficial epidermis. Its inner part cornifies above the mouth of the sebaceous gland and will be shed. 
The connective tissue root sheath (Vagina dermalis radicularis) is continuous with the surrounding connective tissue. The epidermal and dermal root sheaths together with the bulb of the hair constitute the hair follicle. 

The parts of the hair are:
1) medulla
2) the cortex and 
3) the superficial hair cuticle
The arrector pili muscle terminates below the mouth of the sebaceous gland, attaching obliquely to the dermal sheath of the root of the hair. Its contraction results in erection of the hair (in human beings, this brings about the phenomenon of ‘goose pimples’). Contraction of the arrector pili muscle compresses the sebaceous glands and, in erecting the hair, increases the air space between the hairs and the skin surface for thermo-isolation.

The hair coat depends on the breed and is characterized by the individual and group-like arrangement of the hairs, the different portions of the individual hair types (lead hairs, guard hairs, wool hairs) as well as by the density, length and color of the hairs.

There are basically three types of hairs: 
1) The ‘lead’ hair or ‘main’ hair is long, stiff, and slightly curved. It is independent of other hairs and in the dog occurs only rarely. 
2) Guard hairs are shorter than the lead hair, arched near the tip and thickened. Both lead and guard hair types form the hair coat (Capilli). 
3) The third and shortest type of hair is the wool hair. It is very thin, pliable and in its course slightly or strongly undulated. Guard and wool hairs pass in a bundle or tuft together from a compound hair follicle, in which case one guard hair is surrounded by the six to twelve wool hairs that accompany it. The wool hairs predominate in the coat of the puppy. In most canine breeds they lie under the hair coat and only in a few breeds such as the Puli and Commodore, do they project above the hair coat and form a superficial ‘wool coat.’

The color of the hair is effected by the melanin content of the cornified cells as well as the inter- and intracellular air bubbles, especially of the medullary cells. 

The direction of the hairs characterizes the coat. That part of the coat in which the hairs have a uniform direction is called the Flumina pilorum. In a vortex, the hairs are arranged divergently or convergently with respect to a central point. By the crossing of converging lines of hairs, hair ‘crosses’ are formed. 

Sinus or tactile hairs are remarkably long, special forms of hair in the vicinity of the opening of the mouth (Rima oris). To receive tactile stimuli, the root of the hair is ensheathed by a blood sinus that is contacted by numerous sensory nerve endings. Owing to the great lever action of this long hair even the finest tactile stimuli result in stimulation of this receptor. The length of the hairs varies considerably and is dependent on breed. In the ancestors of the dog, who lived in the wild, the longest hairs are found on the dorsum and the shorter ones on the belly and head. But this pattern is mostly lost with domestication. In wild Canidae, the thickness of the hairs increases toward the belly (thickness is about 0.1 mm). 


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