Canine Anatomy & Physiology

Canine Anatomy, Body Parts and Organ Systems

Integumentary System - Skin and Fur

The skin is the largest organ in the body, it has many functions including protection for the underlying organs. The fur helps insulate against heat loss. Dog do not sweat through their skin. They only sweat from their footpads and nose. They lose water by panting rather than sweating 














The dog has three types of muscle

Smooth muscle: not striated - Controls movement of viscera/inside


[The Non-Striated Muscles: (In-Voluntary)

Non-Striated Muscles are a reflex action, which is mostly associated with the Smooth and Cardiac Muscles, which are considered Involuntary or Autonomic they primarily play the part for digestive, respiratory, circulatory, and euro-genital systems.]


Cardiac muscles: striated - makes up the bulk of the heart tissue


[The Striated Muscle forms nearly 1/2 of your pet’s entire body weight.

Skeletal muscles for the most part are considered Voluntary.

Skeletal muscles have the ability for High Elasticity as they provide Contractual support allowing the Dog to perform Lateral, backwards and forward movements with little strain. These muscles for the most part come in pairs and are attached by their extremities to "Two-More" bones. When in action one muscle is fixed this is called the "Origin", movable is called the "Insertion".  Dogs are very agile-flexible this allows for a greater range of movement and stamina. Voluntary muscles are distinguished from one another by various names, which refer to there primary action such as:  (Flexor) bending action. (Extensor) straightening action. Other associations are: Depressors, Constrictors, and Dilators etc.]


Skeletal muscles:   striated - makes up the rest

The function of muscles is to provide movement to the dog’s body. Muscles are made up of two types smooth and striated. Smooth muscles are within the internal organs i.e. intestines, stomach and bladder. The dog cannot voluntary or consciously control these muscles or the cardiac muscles. Skeletal muscles are under conscious control they aid walking, eating or wagging the tail also eye movement, head movement etc.. The dog can control skeletal muscle which can be contracted or relaxed at will. Most muscles consist of bundle of long cells & muscle fibre. Muscles attached to the bones by tendons. The stomach has a very thin covering of muscle. Thigh muscles give explosive energy for chasing. The Hip muscles support the back legs. Tail muscles allow the tail to raise, curl and wag. The neck muscles let the head turn over 220 degrees. Extrinsic muscles are those that you see and are voluntary muscles. The intrinsic muscles control the internal force and action, and extrinsic muscles provide range of movement.


Types of muscles

Strap muscles:   parallel Fibres – The fibres are arranged parallel to the tendon of insertion this results in a greater range of shortening and provides greater movement velocity distance per time. Examples of these muscles are the sternothyroid and sternothoid in the neck.

Pennate muscle:   unipennate – The fibres are arranged at an angle to the direction in which the tendons moves. This results in a greater area of muscle fibres along axes of contraction and produces more strength.

Unipennate:   ulnar & radial heads of digital flexors muscles

Bipennate:   infraspinatus muscle attached to the scapula

Multipennate:   humeral head of the deep digital flexor muscles, deltoid muscle

Most muscles consist of bundle of long cells & muscle fibre. Muscles attached to the bones by tendons. The stomach has a very thin covering of muscle. Thigh muscles give explosive energy for chasing. The Hip muscles support the back legs. Tail muscles allow the tail to raise, curl and wag. The neck muscles let the head turn over 220 degrees.


Skeletal Muscle Groups

Muscles of mastication: operate temporomandibular joint.

The temporomandibular joint connects the lower jaw, called the mandible, to the temporal bone. To close the jaw the dog uses temporal and masseter muscles to open the jaw dogs use digastricus muscles and gravity

Muscles of facial expressions:   move nose, lips, eye lids, ears and skin

Muscles of the pharynx:   (striated muscle) three parts nasopharynx, oropharynx & laryngopharynx 


Tongue Muscles 

Intrinsic: forms tongue this muscles curls and bends the tongue

Extrinsic: moves the tongue in and out

Genioglossus: protracts the tongue

Hyoglossus: retracts the tongue

Styloglossus: retracts the tongue

Lyssa: fibrous tissue enveloping fat & muscle

Eye Muscles

Extrinsic eye muscles: made up of seven muscles

Oculomotor: dorsal rectus, medial rectus, ventral rectus and ventral oblique muscles

Trochlear: dorsal oblique muscle

Abducent: Lateral rectus and retractor bulbi muscles


These connect the muscles to the bones they are tough fibrous bonds of collagen, a fibrous protein called tendons. They may be flat as in the toes or round as in the triceps that connect to the elbow. The tendons must be strong but able to glide freely to ensure easy movement.





The Body

The body of a dog contains most of its vital organs. The heart, lungs, stomach, and intestines are located there. So too are its sex organs, kidneys, and bladder. The 13 ribs of the dog's chest wrap around the heart and lungs. Since these organs influence the animal's speed and stamina, chest size can be an indication of these traits.


All dogs have 27 bones from the skull to the point where the tail begins. The number of tailbones, however, and therefore the length of the tail, varies from breed to breed.

The body may be covered with straight or with wavy hair. Hair shafts emerge from tiny follicles in the skin. The shafts are connected to tiny muscles that cause the dog's hair to stand up, or bristle, when they contract.

During times of stress, a dog raises its hackles--the hair along the neck and spine. Special sensory hairs called whiskers are near the nose, but their usefulness is doubtful because a dog rarely relies on the sense of touch.

The Legs


The front legs and back legs of a dog are also called the forelimbs and hind limbs. A dog uses its legs for movement, for scratching, and, in some breeds, for digging.

Each of the forelimbs is connected to the body by a long, narrow scapula, or shoulder blade. Its lower part, in turn, forms a shoulder joint with the humerus, the upper forelimb bone. The lower forelimb bones, the radius and the ulna, are fused at two points and act as a single bone.


The foot, or paw, has five toes. One of them--the dewclaw--is too high to be of any use. It is a vestigial part and is often surgically removed from puppies. The toes of the foot are composed of a number of bones. A toenail, or claw, emerges from the end of each toe. The foot also has cushiony pads for each toe and two larger pads farther up the paw. Dogs perspire through their pads.


Each of the two hind limbs is connected to the body at the pelvic bone. The upper portion of the femur, or thighbone, fits into a socket in the pelvic bone to form the hip joint. The tibia and the fibula are beneath. They make up the lower thigh. The joint where their upper portions link with the femur is called the stifle. The joint where their lower portions link with the foot bones of the hind limbs is called the hock. Like the forefeet, the hind feet have pads and four functional toes, although a dewclaw is sometimes present.









Osteology - ‘The study of bones’

The dog’s skeleton averages 319 bones. The skeleton is composed of three types

Appendicular skeleton: portion of the skeletal system includes all of the bones contained in the limbs (appendages) of the animal. ... click to view

Axial skeleton: the bones of the skull, spine, ribs and sternum. The axial portion of the skeletal system is located along the longitudinal axis of the animal. ... click to view


Visceral skeleton: bone that forms part of an organ (such as the middle ear ossicles). The bones of the visceral skeleton are formed in soft organs. They are not present in all species of animals. Examples of visceral skeleton bones include: os penis - bone in the penis of dogs


Bones are rigid living organs that have their own supply of blood vessels and nerves. They are made up of minerals, primarily calcium and phosphorous. They make the frame structure of the body. They also protect the delicate internal organs. The skull protects the brain and eyes. The breastplate and ribs protect the heart and lungs. The other bones provide support and locomotion i.e. legs, tail and neck. The bones in the ear provide sound transmission and help the dog to hear. Bones come in different shapes and sizes:-



Long bones: length is greater than the diameter found in the limbs. Bones commonly found in the appendicular skeleton, consisting of a diaphysis and an epiphysis.

Short bones: approximately equivalent dimensions found in the carpus, metacarpus and tarsus, metatarsus.


Flat bones: e.g scapula and many bones in the skull where they surround and protect the eye, ear, sinuses, and brain and they are found in the pelvis where they provide for the attachment of muscles and long bones.

Irregular bones: short and multiple bones e.g. vertebrae and all bones of the skull that are not of the flat type, and three parts of the hip bone.


Sesamoid bones: small bones within tendons e.g. knee cap (patella). Small cuboidal shaped bones associated with tendons and ligaments. These bone reduce wear and tear on the tendons and as they pass over a articulation or prominence.


The outside of a bone is called the cortex made up of minerals and protein. The inside of the bone is marrow. The bones are held together by specialised connective tissues called ligaments. This is called an articulation or joint. Bone ends would grate causing wear and tear if not for the cartilage. Although cartilage is tough it can be damaged by joint stress and trauma. Joints of the hip and shoulder are called ball & socket. The rest of the limb joints are of the hinge type they flex and extend in a plane from front to back. Dogs and humans skeletal anatomy have much in common. One difference – humans carry weight on their hip and the dog carries 75% of weight on his shoulder joints and front end.



Common bone features

Articular surface: a joint surface

Condyle:   a large rounded articular surface

Head: the rounded proximal articular surface of many long bones -- united to shaft by "neck"

Facet: a flat articular surface

Processes: lumps and bumps on bones

tuber, tubercle, tuberosity, trochanter

Holes or Depressed Areas

Foramen: a hole in a bone

Fossa: a depressed area on a bone

Arthrology ‘The study of joints’

Ligaments connect bone to bone generally found across joints. Joints are where two bones meet the ends covered by a layer of smooth cartilage.

Fibrous joints: immobile joints joined by fibrous tissue.

Suture:   undulating seams between bones of the skull



Gomphosis:   tooth in an alveolus, united by periodontal ligament (see teeth diagram)

Syndesmosis: bones joined by ligaments, e.g., radius, ulna, tibia and fibula long bones running parallel.

Cartilaginous joints: immobile joints joined by cartilage.

Symphysis: fibrocartilage union e.g. pelvic symphysis, mandibular symphysis

Synchondrosis: hyaline cartilage union, e.g., physis

Synovial joints: mobile joints, fibrous tissue enclosing a synovial cavity

Simple joint: formed by two bones, e.g., shoulder joint

Compound joint: formed by more than two bones, e.g. elbow joint

Hinge joint: movement in one plane

Ball & socket joint: capable of circumduction

Plane joint: gliding action, e.g., vertebral articular





The Head

There are two basic head shapes--a narrow skull with a long face and a wide skull with a short face--plus several intermediate head shapes. Long-faced dogs, such as the German shepherd and the cocker spaniel, may have jaws eight inches long. By contrast, the nose of small-faced dogs, such as the Pekingese and the pug, may be less than an inch from the eyes.


Dogs have 42 teeth. Six pairs of sharp incisor teeth are in front of the mouth, flanked by two pairs of large canine ("dog") teeth. The other teeth are premolars and molars. The incisors and the canines are very important because the dog bites and tears at its food with these teeth.

Air breathed in through the dog's nose passes on its way to the lungs through the two nasal cavities behind the nose. These cavities are lined by a mucous membrane containing many nerve endings stimulated by odors. Smell is the dog's most acute sense. A dog continually sniffs the air, the ground, and nearby objects to learn what is happening around it. The indentation in the dog's forehead just above eye level is called the stop. The stop in some dogs is deeper than that in others.


The fairly thin tongue of the dog is used mainly for guiding food to the throat, for licking the coat clean, and for perspiration. When a dog is overheated, it cools off by hanging its tongue out and panting. As it pants, the evaporation of perspiration from its tongue cools the animal. The dog also sweats through the pads on its paws and--slightly--through its skin.

A dog's ears either stick up or hang down. The earliest dogs probably had erect ears, but the ears began to droop in smaller, later breeds because of excessive ear skin. Dogs have a fine sense of hearing. They can hear sounds at frequencies too high for people to hear. This is why dogs can respond to "silent" whistles.


Each eye of a dog has three eyelids, the main upper and lower lids and a third lid hidden between them in the inner corner of the eye. The third eyelid can sweep across the transparent cornea of the eye and clean it like a windshield wiper.


The head and body of a dog are connected by its neck. The neck may be long or short, depending on the size of the seven bones that support it. The length of the vocal cords in the neck is a factor influencing the pitch and loudness of a dog's voice--its barks, grunts, and howls.


The cardiovascular system - Heart and Blood Vessels 

Includes the heart and blood vessels and performs the function of pumping and carrying blood to the rest of the body.

The blood contains nutrients and oxygen to provide energy to allow the cells of the body to perform work.  








The Lymphatic System - Lymph Nodes and Lymph Vessels

Includes the lymph nodes and lymph vessels.  The lymphatic system is part of the immune system that helps the body fight off desease.  The lymphatic system also works with the cardiovascular system to return fluids that escape from the blood vessels back into the blood stream.





The Musculoskeletal System includes all the muscles, bones and joints.












 The Nervous System - includes the brain, spinal cord and all the nerves that communicate between tissues and the brain and spinal cord.


normal vertebral column and spinal cord                                                                           prolapsed intervertebral disk






 The Respiratory System  includes the mouth, nose, trachea and lungs.  The Respiratory system is responsible for taking in oxygen and eliminating waste gases like carbon dioxide.  Beacuse dogs and cats do not sweat through the skin, the Respiratory system also plays an important role in regulation of temperature.








 Special Senses of the Dog allow the animal to interact with its environment; sight, taste, smell and hearing. 





Urogenital System - Kidneys, Urinary Bladder, Genitals, Ureters, Urethra. Responsible for removing

 waste from the blood and eliminating urine. Genital organs determine sex and reproduction.







The digestive system includes the: mouth, teeth, salivary glands, esophagus, stomach, small intestine, large intestine, pancreas, liver and gall bladder

The digestive system absorbs and digests food and eliminates solid wastes from the body.   


Mouth: Digestion begins in the mouth where food is mixed with saliva to lubricate the food as it passes down the esophageus. Dog's teeth are suited for gripping, tearing and shredding the food. (Go here to Canine Dental Anatomy). Dog's saliva does not contain enzymes for digesting carbohydrates, like humans who have amylase.





Stomach:  Swallowed food passes down the esophageus to the stomach. The stomach of a canine is very acidic with a pH as low as 1. Food is well mixed and broken down before contents leave the stomach as chyme




Small Intestine:  Chyme is fluid that passes easily into the the small intestine, where the pancrease provides additional digestive enzymes. These enzymes continue protein digestion and also provide carbohydrate and fat digestion.




Large Intestine:  Most of the nutrients have been digested and absorbed by the time any food reaches the large intestine. It is were water is absorbed and bacteria can break down undigested fibre.

















THE BODY OF A DOG   Dogs grow to various sizes. The Irish wolfhound, for example, stands about 32 inches high at the withers, or top of the shoulders. The chihuahua, however, stands about five inches.


The color of a dog's coat, or hair cover, also ranges widely, even within a breed. Some dogs are all black. Others are all white. Some have light markings on portions of their bodies and darker coloration elsewhere. Or, they may have a solid color other than black. All dogs have some hair cover, even the so-called hairless ones.


The shape of a dog is determined by three major structures--the head, the body, and the legs. The size and form of these structures vary greatly as do, for example, coloration and hair characteristics.



 Growth plates for dogs close on the average at:

Proximal epiphysis of the humerus 10 to 13 months

Distal epiphysis of the humerus 6 to 8 months

Proximal epiphysis of the radius 6 to 11 months

Distal epiphysis of the radius 8 to 12 months

Olecranon of the ulna 6 to 10 months

Distal epiphysis of the ulna 8 to 12 months

Proximal epiphysis of the femur 7 to 11 months

Trochanter major of the femur 6 to 10 months

Trochanter minor 8 to 13 months

Distal epiphysis of the femur 8 to 11 months

Lateral condyle of the tibia 6 to 12 months

Distal epiphysis of the tibia 8 to 11 months

Proximal epiphysis of the fibula 8 to 12 months

Distal epiphysis of the fibula 7 to 12 months


The images on this page have been reprinted with permission by the copyright owner, Hill’s Pet Nutrition, Inc.  These images should not be downloaded, printed or copied.

Contact Details

Jenni Hogan-Rees
Bacchus Marsh, VIC, Australia
Email : [email protected]