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The hand (forefoot, forepaw, manus) is made up of the carpals (wrist bones), the metacarpals, and the digits (fingers/toes). The carpus contains two horizontal rows of small, somewhat cube-like bones, ranging from six in the artiodactyls, seven or eight in the horse, to eight in the cat, dog, and human. Most evident in the horse, the flexed wrist separates into three forms in front. From the top downward, they are the lower end of the radius, the top row of the carpals, and the bottom row of the carpals, which are fused by ligaments to the top of the single metacarpal. These bones are all hinged to each other in back. The accessory carpal bone (pisiform bone), part of the upper row of carpals, projects backward from the outer back portion of the wrist. Most noticeable in the horse, a strong ligament that passes downward and forward from this bone to the top of the outer metacarpal participates in creating the leg profile.

ELBOW JOINT

ELBOW JOINT

ANATOMICAL WRIST (CARPAL BONES) Upper row Lower row

Equine Assessory Carpal Bone

STANDING

LEFT FRONT LIMB

OUTSIDE VIEW < FRONT

(ALL AFTER ELLENBERGER)

LEFT FRONT LIMB OUTSIDE VIEW ■4 FRONT

ANATOMICAL WRIST (CARPAL BONES) Upper row Lower row

STANDING

LEFT FRONT LIMB

OUTSIDE VIEW < FRONT

(ALL AFTER ELLENBERGER)

LEFT FRONT LIMB OUTSIDE VIEW ■4 FRONT

The metacarpals form the body of the hand (palm and back of hand). They can vary considerably—by their relative size, by some being absent, or by being fused together. Metacarpals are counted from one through five, beginning with the medial (inner, thumb) side. Primates have five developed metacarpals. Dogs and cats have five, with the first one reduced substantially and the second and fifth reduced slightly. This makes the two middle metacarpals, numbers three and four, the longest, descending lower than the adjacent ones. This in turn causes the first phalanges of toes three and four to lie more horizontally than those of toes two and five, which slope downward.

Some artiodactyls, such as the ox, deer, goats, and sheep, have well-developed third and fourth metacarpals, which are fused together throughout their length into a single strong bone, and are weight-bearing. Their metacarpals two and five are reduced in various ways or missing according to the different species, whereas the first metacarpal is always absent. In the horse, the third (middle) metacarpal, called the cannon bone, is very large and weight supporting. The second and fourth are much reduced, and the first and fifth are missing. Metacarpals that are reduced often have a well-developed head at their upper end and taper to a sharp or rounded point at their lower end. They are called splint bones.

Except for the first digit, each digit, or finger, typically contains three phalanges—a proximal phalanx that articulates with the bottom end of a metacarpal, a middle phalanx, and a distal phalanx whose shape conforms to the attached hoof, nail, or claw. The horse's proximal phalanx is called the pastern bone. The lower portion of its middle phalanx, as well as its distal phalanx (the coffin bone), is buried within the structure of the hoof.

The first digit (thumb) has only two phalanges—a proximal and a distal—and when present in four-legged animals, such as the dog and feline, it is reduced in size and doesn't touch the ground. In primates, the thumb is the shortest, heaviest finger, and is opposable to the other fingers (can touch the other four fingers). Monkeys have long slender digits on the hand and foot. Apes and humans have long fingers on the hand and short toes on the foot.

Felines have a ligament connecting the distal phalanx (which supports the claw) to the lower end of the middle phalanx, which keeps the claw pulled back (retracted) in the relaxed position. The distal phalanges have to be actively flexed by muscles to extend the claws. This ligament keeps the claws off the ground when felines are walking, keeping their tips sharp. When retracted, the distal phalanx becomes inclined from the vertical, being directed upward and outward (overlapping the outside of the middle phalanx). In dogs, the tip of the claw normally rests on the ground.

In the ungulates (hoofed animals), the three phalanges of a digit typically incline downward and forward in a straight line. Exceptions are the goat and some other hoofed animals, whose proximal phalanx is inclined but whose middle phalanx is directed straight downward, giving the foot a distinctive shape.

Sesamoid bones are small bones, located behind a joint, which add mechanical advantage to a tendon by acting as a pulley and pushing a tendon slightly away from that joint. They are often located behind the metacarpophalangeal joints, where they have an effect on the profile of the limb. They are usually present at other joints of the phalanges, but they do not affect surface form.

An important difference between the various species is the number of digits (fingers or toes) per hand or foot. Because the metacarpals are covered by skin and their number per foot is usually hidden, the exposed individual fingers or toes must be carefully counted. A horse has only one toe per limb, cows have two, rhinos three, pigs four, cats and dogs have five in the forelimb (one very reduced) and four in the hind limb, and primates have five all around. Interestingly, the extinct Devonian amphibian-like Acanthostega had eight digits per limb, making that the maximum number of fingers or toes found in the hand and foot. Missing digits in all descending species were lost through evolution.

RADIUS

RADIUS

Line Drawings Human Rib Cage
HUMAN

RADIUS

RADIUS

Sheep Front Leg Anatomy

LEFT MANUS ("HAND") OF FRONT LIMB • FIRST DIGIT ("THUMB") IS LOCATED ON RADIAL SIDE OF LIMB • FRONT VIEW C Carpus; M Metacarpal; P Phalanx

Equine Anatomy The Front Limb

LEFT MANUS ("HAND") OF FRONT LIMB • FIRST DIGIT ("THUMB") IS LOCATED ON RADIAL SIDE OF LIMB • FRONT VIEW C Carpus; M Metacarpal; P Phalanx

(DOG, OX, AND HORSE AFTER ELLENBERGER; PIG AFTER NICKEL)

First Phalanx Dog
CWW EXTENDEO
Haunch Bone

CLAW RETRACTED LAST TOE BONE OVERLAPS OUTSIDE OF MIDDLE TOE BONE

FELINE

LEFT FRONT TOE AND CLAW

OUTSIDE VIEW

CLAW RETRACTED LAST TOE BONE OVERLAPS OUTSIDE OF MIDDLE TOE BONE

(AFTER ELLEHBERGER)

Pelvis

The pelvis consists of the two hip bones (haunch bones) of each side of the body. They are attached to each other at the midline below, and to the intervening sacrum above. The pelvis consists of three bones—the ilium, ischium, and pubis—which are all fused together in the adult. They meet at the side of the pelvis where they form a socket, called the acetabulum, which receives the head of the femur to form the hip joint. Notice the tilt of the pelvis in the various animals by comparing the relationship between the point of the hip on the outside front corner with the ischiatic tuberosity in back. The pelvis of the ox is more horizontal than that of the horse.

The front portion of the pelvis expands into the wide, flat ilium (plural, ilia). The anterior plate-like portion faces upward in the horse and ox and outward in the dog and cat. It is especially narrow (seen in side view) in the cat. Its front edge, called the crest, is usually curved. The crest is concave in the horse and ox where it is covered over with muscle—concealed in the horse but occasionally visible through the muscle in the ox. It is convex and just below the skin in the dog, cat, pig, and human (where it is not crossed over by muscles). The ends of the crest terminate above and below into bony landmarks whose prominence on the surface varies by species. The point above, at the sacrum, is called the sacral tuberosity—single with a rounded point in the horse and cow, and double, but very subtle, in the dog and cat. The lower point, located toward the outside and forming the point of the hip, is called the coxal tuberosity. It forms a simple point at the end of the crest in carnivores, a knobby expansion in the ox, and a more complicated, elongated swelling in the horse. It is most prominent on the surface in life in the ox, visible in the horse, and subtle in carnivores.

The rear portion of the pelvis is called the ischium. Its posterior projection expands into the variably shaped ischiatic tuberosity—three-pointed in the ox; elongate in the dog and horse. Called the angle of the buttocks, it can be visible on the surface in the ox, sheep, goat, and carnivores because the rear thigh muscles originate from its lower edge, leaving the upper edge exposed. In the horse, the ischiatic tuberosity is covered and concealed by the semitendinosus muscle. In the horse and ox, the width across the ilia is substantially greater than that across the ischiatic tuberosities. In the carnivores it is the opposite, with the ischiatic tuberosities slightly wider than the ilia.

The pubis, located medial to the hip socket, meets its fellow of the other side to fuse for a short distance on the midline. Although typically not seen directly in four-legged animals, it is the termination of the lower profile of the belly as the abdominal muscles (rectus abdominis) gain attachment to the front edge of the pubis.

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Responses

  • anja
    Where is the equine carpal bone anatomy?
    8 years ago
  • carol
    How many digits per foot is weight bearing in a pig?
    8 years ago
  • vigo
    What are the joints in a goat carpus?
    8 years ago
  • celendine
    How many carpal bones in a horses carpal joint?
    7 years ago
  • sm
    What bone is just proximal to the carpus but below the elbow in dogs?
    7 years ago
  • krystal
    How do the carpals (wrist bones) differ, in the bat, human, and horse?
    7 years ago
  • Arabella
    What are short boned in a pig skeleton?
    4 years ago
  • william
    Why 1st metacarpal is absent in horse?
    4 years ago
  • Sara
    How many metacarpals in animals?
    2 years ago
  • melampus
    What is accesory carpal of the goat?
    2 years ago
  • Wiseman
    How does the structure of the hind limb differ in apes , dogs , sheep and horse?
    1 year ago
  • john
    What animal has five toes?
    7 months ago
  • michael
    Which animals have five toes per limb?
    7 months ago
  • Taimi
    What animal has five toes per limb?
    7 months ago

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