The animal body is divided into different regions for anatomical description and easy learning. In most quadrupedal mammals, the bodies and limbs have certain structural similarities. Thus, they also have similar body regions.
Though bodies and limbs are seemingly different in the pig and the horse, recognition of the commonalities can make the study of multiple species much simpler.
Here, we will learn the animal body regions with the example of horse anatomy. But this guide is also applicable to most of the domestic and wild species.
Common regional terms used in animals
First, let’s see the terms that are used to identify regions of the trunk and limbs are shown in the Table and Figure.
| Terms | Meaning |
| Barrel | Trunk of the body—formed by the rib cage and the abdomen |
| Brisket | Area at the base of the neck between the front legs that covers the cranial end of the sternum |
| Cannon | Large metacarpal or metatarsal bone of hoofed animals |
| Fetlock | Joint between cannon bone (large metacarpal/metatarsal) and the proximal phalanx of hoofed animals. |
| Flank | Lateral surface of the abdomen between the last rib and the hind legs |
| Hock | Tarsus region |
| Knee | Carpus of hoofed animals |
| Muzzle | Rostral part of the face is formed mainly by the maxillary and nasal bones |
| Pastern | Area of the proximal phalanx of hoofed animals |
| Poll | Top of the head between the bases of the ears |
| Stifle | Femorotibial/femoropatellar joint— equivalent to a human knee |
| Tailhead | Dorsal part of the base of the tail |
| Withers | Area dorsal to scapulas |
These common regional terms give us a shorthand way of recording anatomic locations in veterinary records. It is easier to refer to the “fetlock” of a horse than to have to write “the joint between the large metacarpal or metatarsal bone and the proximal phalanx.
The body’s limbs, trunk, and head exhibit bilateral symmetry. This means that the right and left sides of the body are mirror images of each other.
Similar right and left structures are called a paired structure. They have the same relationship as a pair of gloves in that they are similar but not interchangeable.
Organs within body cavities, in contrast, are often unpaired and are not symmetrical; examples include the heart, liver, and intestines.
Animal body regions
The animal bodies (horse/others) are divided into the following regions –
- The head and ventral neck region
- Neck and vertebral column region of the animals/horse
- Thorax region of the animals/horse
- Abdominal region of the animals/horse
- Pelvic region of the animals/horse
- Forelimb region of the animals/horse, and
- Hindlimb region of the animals/horse
Head and ventral neck region of the horse
The age and the breed determine the common character of the head. In young foals, the cranial cavity is domed to match the contours of the brain.
The older conformation develops as the face lengthens and deepens. It accommodates the full complement of teeth and expanding paranasal sinuses.
Nostril and eye
The nostrils are large and widely spaced, which is imposed by the supporting alar cartilages. Again, the upper part of the opening leads to a blind nasal diverticulum that occupies the nasoincisive notch.
The lower part leads directly to the nasal cavity. It is therefore essential when a stomach tube is passed to ensure that it is guided into this lower part.
The entrance to the mouth is small, and the commissure is a little in front of the first cheek teeth. Short, fine hairs sparsely cover the skin of the lips and the adjacent part of the muzzle. The lips are both mobile and sensitive and are used in the selection and prehension of food.
The eyes are prominent and placed to each side of the head, enjoys a panoramic field of vision. Indeed, horses may view almost all around by making only slight movements of the head.
Eyelids and tarsal glands
The upper and lower eyelids and adjacent skin carry a few scattered tactile hairs. The palpebral skin is thin and, being loosely attached, is thrown into folds when the eye is open.
The tarsal glands, which open at the junction of the skin with the conjunctiva. They are about 50 in the upper lid, rather fewer below, and are clearly visible in palisade formation when the lids are everted.
The palpebral conjunctiva is well vascularized, the bulbar part less generously; the bulbar conjunctiva is strongly pigmented toward the corneoscleral region.
The third eyelid in the medial angle can be exposed in the usual way by pressing on the eyeball through the upper eyelid.
The neck and vertebral column region of the horse
The neck may be arched, straight, or hollowed in the natural standing posture. The arched form, known to horse riders as a swan- or peacock-neck, is characteristic of certain breeds.
The transition between the neck and withers may be smooth or marked by a dip. In saddle horses, the neck deepens considerably toward the chest, but the change is usually less marked in the heavier draft breeds.
The heavy neck of the stallion is mainly due to the strong development of the fatty fibrous tissue dorsal to the nuchal ligament.
Cervical vertebrae
The course of the cervical vertebrae may not be evident on simple scrutiny. However, the wing of the atlas is almost always a prominent, visible and palpable landmark.
The positions of the transverse and articular processes of the third to sixth neck vertebrae may be visible in animals that are lean or in poor condition.
These features are usually detectable on palpation, although in fat or particularly well-muscled horses.
In thin-skinned horses, certain of the superficial muscles stand out as individual surface features when tensed. The great length of the spinous processes of the second to ninth thoracic vertebrae, but the region also embraces the scapular cartilages and associated muscles.
Withers and lions of the horse
The withers vary considerably, and in saddle animals, it is preferred that they be both high and long and of moderate width. Behind the withers, the line of the back is more or less straight, and though it slopes up somewhat toward the croup.
The caudal part/loins tends to be broader and flatter and merges with the flanks without a sharp change. The transverse processes of the horse’s lumbar vertebrae are not palpable.
The spinous processes of the horse’s lumbar and caudal thoracic vertebrae may be palpated. A median groove between the muscles of the loins and croup is most marked in draft animals.
Thorax region of the horse
The impression of the thoracic cavity from simple inspection of the exterior is increased by the height of the withers and the caudal prolongation of the rib cage. The shoulder and arm completely cover the narrow cranial part of the thorax. Some variation in the projection of the limb bones on the thoracic skeleton is due to the inconstant slope of the scapula. The humerus forms a lesser angle with the horizontal than in the smaller species. Thus, this brings the elbow within the skin of the trunk.
The precise position of the elbow joint is not immediately apparent. The massive triceps muscle completely occupies the triangle between the scapula and humerus.
There are 18 pairs of ribs, where the most caudal ribs may even provide visible landmarks. The first rib, the shortest of all, is almost vertical. An exact appreciation of the position of the diaphragm is essential for the clinician.
Abdomen region of the horse
The extent of the abdomen is not immediately apparent because a large part is concealed within the rib cage. Here, the flank is reduced in size by the caudal inclination of the ribs.
Abdominal conformation varies much with age, condition, and the amount and nature of the rations. The ventral contour is especially variable; it slopes gradually between the sternum and the pubic brim in animals in hard condition.
The trunk is broadest at the last ribs. The upper part of the flank sinks in to form a paralumbar fossa, but the relative shortness of the region behind the ribs makes this feature much less obvious than in cattle.
The lower part of the belly is rounded from side to side, except in foals, in which the whole abdomen is slabsided and shallow.
The position of the last rib is often visible, but most other skeletal boundaries of the flank and floor are less easily found. The transverse processes of the horse/animal’s lumbar vertebrae are usually too deeply buried under muscle to be palpable.
The dorsal part of the coxal tuber is very conspicuous. Still, the ventral part, which gives origin to the internal oblique and tensor fasciae latae, is not visible, although it is easily palpable.
Pelvis region of the horse
The pelvic cavity is roofed by the sacrum and the first two or three caudal vertebrae. Here, the roof narrows from front to back and is slightly concave in its length.
The ischial tuber and spine are both less prominent than in cattle, and the contribution of the sacrosciatic ligament to the lateral wall.
The floor is solid because the symphysis is firmly fused in mature animals. It is more or less horizontal and flat in its length, though somewhat hollowed from side to side.
The entrance to the pelvic cavity faces cranioventrally. Its slope places the pubic brim below the third, or even fourth, sacral vertebra in the mare but only the second in the stallion.
Viewed from the front, the inlet to the female pelvis is wide and rounded. But in the male, it is more angular and cramped, particularly ventrally. In both animals, the outlet from the cavity is much smaller than the inlet. A caudal vertebra bounds it, the free edges of the sacrosciatic ligaments, and the ischial tubers and arch.
The cavity has the approximate form of a truncated cone. Here, the pelvis of the mare is thus more favorably formed for ease of parturition than that of the cow.
Perineum region of the horse/animals
The most distinctive feature of the perineum is its confinement between the semimembranosus muscles. These muscles cover the ischial tuberosities and also the ischiorectal fossae.
The thin, sparsely haired, and deeply pigmented perineal skin obtains a surface sheen from the secretion of sebaceous glands. In males, the urethra may be palpated where it bends around the ischial arch. The deeper structures of the perineum closely resemble their bovine counterparts.
Forelimb region of the horse
The limbs of the horse display extreme adaptations for fast running with a concomitant loss of versatility. However, both forelimbs and hindlimbs find their main, indeed almost exclusive, employment in supporting the body.
It is the forelimbs that carry the greater part of the body weight at rest. They also supply the principal shock absorbers that are necessary in the faster gaits, and especially when landing from a jump.
A forelimb with good conformation is straight when viewed from the front. A line dropped from the point of the shoulder bisects the limb and passes through the center of the hoof.
Deviations from the normal conformation can result in abnormal movements. It may cause interference between the feet, unequal and abnormal hoof wear, and the development of lameness.
Hindlimb region of the horse
Although the hindlimbs support little more than 40% of the body weight, they supply by far the greater part of the forward impetus in locomotion.
This thrust is delivered through the hip and sacroiliac joints, which are intrinsically more stable than the shoulder of the forelimb. Tight ligaments strengthen the sacroiliac joint.
The muscles of the croup and thigh well support both the sacroiliac and hip joints. These muscles are particularly massive in the horse, in which they round the contours distinctively.
Despite the muscular development, the coxal tuber remains a conspicuous landmark that is palpable in its whole extent and visible in its upper part. The sacral tuber is difficult to palpate in most animals and rises a little above the level of the adjacent spinous processes.
The ischial tuber is also not always easy to appreciate. Its location and a general impression of its form may be obtained on deep palpation over the muscles of the croup and thigh.
The position of the hip joint cannot be determined directly. It may be deduced from its relationship to the greater trochanter of the femur.
Conclsuion
The animal body is divided into head, neck, thorax, abdomen, pelvic and limb regions for anatomical description and easy learning. Student must identify the different regions of the animal’s body before starting their anatomy learning.
References
- Dyce and Wensing, Textbook of Veterinary Anatomy, 4th edition, Saunders, USA.
- Beth Vanhorn and Robert W. Clark, Veterinary Assisting: Fundamentals & Applications, ISBN-13: 978-1-4354-5387-6, Maxwell Drive, Clifton Park, NY 12065-2919 USA.
- Anna Dee Fails and Christianne Magee, Anatomy and physiology of the Farm Animals, 111 River Street, Hoboken, NJ 07030, USA.
- Hilary M. Clayton, Peter F. Flood, Diana S. Rosenstein, and David Mandeville, Clinical Anatomy of the Horse, First edition 2005, ISBN 07234 3302 X.
- Pasquini and Spurgeon, Anatomy of domestic animals, systemic and regional approaches.
- Victoria Aspinall B, and Melanie Cappello, Introduction to Veterinary Anatomy and Physiology Textbook, ISBN 978-0-7020-5735-9, Elsevier.
