Sheep Anatomy: Labeled Diagrams and 3D Model of a Sheep

The external parts of a sheep are the named regions that farmers, show judges and vets use: the poll, forehead, face and muzzle on the head; the neck, top of the shoulder, back, loin, hip, rump and dock along the top line; the ribs, flanks and belly on the side; and the forearm, knee, cannon, pastern, dewclaw, stifle, hock and leg on the limbs.^{[12, 11]}

Sheep also have three kinds of skin gland that goats lack: an infraorbital pouch below the inner corner of each eye, an interdigital gland shaped like a tobacco pipe between the two claws of every foot, and a pair of inguinal pouches beside the udder.^{[26, 11, 28]} The interdigital gland stores a thick, oily secretion and empties it onto the skin through a duct. The duct can become blocked, swelling the pouch, which rarely causes lameness; the gland can also become infected.^[30] A ram has a raised "knob" on the nose just above the nostrils.^[11]

A sheep has the same organ systems as other mammals, built around a stomach of four compartments that fills most of the left side of the abdomen.^{[4, 3]} This page describes an adult Suffolk, a meat breed with a white fleece and a black, wool-free head and legs; Suffolks of both sexes are naturally polled (hornless).^{[14, 15, 16]} Other breeds differ in size, fleece, horns and tail, but have the same organs. Vets use four direction words for a standing animal: cranial (towards the head), caudal (towards the tail), dorsal (the back) and ventral (the belly).

Sheep body by the numbers

Normal ranges differ between sources because they measure different flocks and conditions; a sheep that seems unwell should be seen by a vet.

Inside a sheep, the chest holds the heart and lungs in front of the diaphragm, and the abdomen behind it is dominated by the stomach: the rumen lies against the left body wall, while the liver lies on the right against the diaphragm and the intestines fill much of the right side.^{[1, 4]} The bladder and the reproductive tract sit at the entrance to the pelvis, with the bladder below the uterus in ewes.^[1]

A sheep has one stomach with four compartments, not four stomachs: the rumen, reticulum and omasum make up the forestomach, and the abomasum is the true stomach.^{[3, 6, 2]} Swallowed grass goes into the rumen and reticulum, where microbes ferment the fibre; the sheep brings it back up as cud, chews it again and swallows it, and the gas from fermentation is burped up.^{[3, 6]}

1. Rumen (paunch): the largest compartment, a fermentation vat filling most of the left abdomen. In sheep its papillae are large and tongue-like. The dorsal sac is the longer of the two sacs, but the ventral sac is larger, reaches further to the right than in cattle, and its caudal blind sac extends further back than the dorsal one.^{[4, 5]}
2. Reticulum (honeycomb): the front compartment, lined with honeycomb ridges and lying against the diaphragm.^{[3, 1]} In lambs the reticular groove sends milk straight to the omasum and abomasum, past the rumen.^[3]
3. Omasum ("many piles"): a round compartment packed with leaves of tissue. The leaves give it a large surface that absorbs water from the digesta before it passes to the abomasum; relatively little digestion happens here.^{[3, 6]}
4. Abomasum (true stomach): secretes enzymes and acid like the stomach of a pig or a person.^{[6, 3]}

In a mature sheep the rumen holds about 5 to 10 gallons (roughly 19 to 38 litres), far more than the other three compartments, and the small intestine is about 80 feet (24 m) long.^[6] In smaller ruminants such as sheep, the rumen makes up about 75% of the stomach's volume, the reticulum 8%, the omasum 4% and the abomasum 13%.^[4]

The proportions differ from a cow's: in sheep the reticulum and abomasum are relatively larger and the omasum relatively smaller.^{[4, 5]} A young lamb lives on milk, which the reticular groove sends past the rumen until the forestomach develops.^{[3, 6]} For the inside of each compartment, the rumen pillars and how rumination works in detail, see the cow digestive system guide, which covers the same four compartments in cattle.

An adult sheep has 32 teeth and no upper front teeth: the front of the upper jaw is a hard dental pad, and the eight lower front teeth (three pairs of incisors and a pair of canines shaped like incisors) clip grass against it.^{[9, 10, 7]} Further back, each side of each jaw has three premolars and three molars that grind the food and cud.^{[10, 2]} A lamb has 20 temporary teeth, including four pairs of milk teeth at the front.^{[7, 2]}

Ages from New Mexico State University and Sheep 101; eruption can vary by about six months with breed and diet.^{[9, 8]} A sheep that has lost or broken front teeth is "broken mouthed", and one with none is a "gummer".^[7]

A sheep's spine usually has 7 cervical, 13 thoracic, 6 lumbar and 4 fused sacral vertebrae, followed by about 16 to 24 tail vertebrae.^{[17, 18, 19]} Extra vertebrae are fairly common: a 14th pair of ribs is common, and a 2024 study notes that extra thoracic or lumbar vertebrae are common in Mongolian sheep.^{[20, 19]}

Each leg ends in two weight-bearing digits. The cannon bone of the foreleg is the fused third and fourth metacarpals, and in the hind leg the fused third and fourth metatarsals; the lower ends stay separate, one for each claw.^{[24, 25]} The "knee" of a sheep is its carpus (wrist), and the hock is the joint of the tibia, tarsal and metatarsal bones.^[11] Sheep nasal bones are pointed at the front, unlike the notched nasal bones of cattle.^[22]

Horns, where present, grow on a bony core from the frontal bone covered by a keratin sheath, and in sheep they sit close to the eye socket.^{[23, 21]} Whether a sheep is horned depends on breed, sex and genes at a single locus: in breeds of Central and Western European origin a sheep with one copy of the horned variant is horned if it is a ram and polled if it is a ewe, while in southern European and African breeds the pattern is less consistent.^[23] Tails also vary by breed, from thin to fat and from short to long, and many lambs are docked.^{[11, 13]}

The 3D model does not show muscles, but the main muscles that move a sheep are in the limbs and along the spine. In the foreleg they include the brachiocephalicus, trapezius, latissimus dorsi, deltoid and triceps brachii.^[70] The hind leg (the gigot, sold as leg of lamb) holds the biceps femoris, semitendinosus, semimembranosus and the quadriceps group, with the gluteal muscles over the hip and rump and the gastrocnemius at the back of the lower leg, above the hock.^{[70, 71]} Epaxial muscles above the vertebrae steady the spine and move the neck and back up and down and from side to side, while hypaxial muscles below the spine flex the neck and back.^[70]

A sheep's heart lies low in the chest between the lungs, roughly from the 3rd to the 6th rib (the 2nd to 5th intercostal spaces in Akkaraman sheep), and its caudal edge can touch the diaphragm.^{[1, 36]} In sheep the right coronary artery is much smaller than the left.^[36] The aorta leaves the left ventricle and runs back under the spine, the pulmonary trunk carries blood from the right ventricle to the lungs, and the caudal vena cava returns blood from the back of the body to the right atrium.^[37] For the chambers, valves and vessels on a real heart, follow the sheep heart dissection guide.

A sheep's left lung has two lobes, a cranial lobe in two parts and a caudal lobe, and its right lung has four: cranial (in two parts), middle, caudal and accessory.^{[34, 1]} As in cattle, the bronchus to the right cranial lobe leaves the trachea itself, before it divides; this tracheal bronchus is absent in cats, dogs and horses.^{[35, 34]} Lung abscesses are a common internal form of caseous lymphadenitis, which in sheep more often affects the internal organs than the skin nodes.^[60]

Sheep kidneys are smooth and bean-shaped, like a dog's, not divided into lobes like a cow's, and inside each has a single fused, crest-like papilla instead of many.^{[32, 1, 33]} The left kidney hangs against the rumen and a full rumen can push it right of the midline.^{[1, 32]} The ureters run to the ovoid bladder and pass obliquely through its wall.^[1] In rams the urethra continues past the tip of the penis as the urethral process, where urinary stones often lodge, especially in castrated males.^{[1, 2]}

The sheep brain is remarkably similar to the human brain, which is why it is the standard brain dissected in anatomy labs; its cerebrum is proportionately smaller and its brainstem lies further back.^[59] The cerebrum handles the higher functions, the cerebellum coordinates movement and balance, and the brainstem links the brain to the spinal cord and helps regulate breathing and the heart.^[40] For every structure a lab sheet asks you to label, use the sheep brain dissection guide.

Sheep eyes sit on the sides of the head and have large, horizontal, roughly rectangular pupils. Together these give a very wide field of view, commonly about 270 to 320 degrees and less in sheep with heavy wool on the face, so a sheep can scan its surroundings with only slight head movement.^{[72, 73]} Both eyes see the same scene only in a narrower zone in front, and that is where sheep judge depth well; they often stop to look closely at something unfamiliar before moving on.^{[73, 72]} Sheep also have an excellent sense of smell, which helps rams find ewes in heat and ewes find their own lambs.^[72]

Wool fibres are secondary (undercoat) hairs: the woolly skin has mostly compound follicle groups, while the face, lower legs and ears have mostly simple follicles.^[31] Lanolin is the yellow grease in the fleece, made by the skin.^[13] Thanks to the fleece, adult sheep tolerate heat and cold well, but newborn lambs and newly shorn sheep can easily get too cold.^[2]

The spleen is a flat, triangular, bluish-red organ on the left side, attached to the rumen; a goat's is roughly four-sided.^{[45, 46]} The submandibular, parotid, prescapular and prefemoral lymph nodes are the usual sites of caseous lymphadenitis abscesses.^[60]

A ewe has an udder of two glands with one teat each, and a uterus with two horns; a ram has two testes in a woolly scrotum in the groin and a penis with an S-shaped bend.^{[49, 51, 56]}

Ewe lambs reach puberty at about 6 to 9 months, depending on season and nutrition.^{[68, 67]} Scrotal size is measured in a ram's breeding soundness exam because testis size is closely linked to sperm output.^[58] Where horns occur, they are usually a feature of rams.^{[11, 23]} In the 3D model, the Female/Male switch shows each set of organs on the same Suffolk body.

Sheep and cattle are both ruminants with the same four-compartment stomach, the same dental formula and no upper incisors, so most of their anatomy matches; the differences are in proportions, the kidneys, the udder, the placenta and the male tract.^{[2, 3]}

Explore the cow in 3D on the cow anatomy page.

This is the text version of the 3D sheep: all 82 labeled structures, grouped by body system, with where each is and what it does. Structures marked "females only" or "males only" appear when you switch sex in the viewer.