When you hear the words Bull Terrier anatomy your mind might immediately go to the various Bull Terrier Standards used around the world. Standards do present a positive picture of how the Bull Terrier should look. However, the function of bone structure with muscular structure reveals what is going on underneath the skin. From the egg shaped head to its tapered, fine-pointed tail, the Bull Terrier is a compact combination of keen intelligence, powerful muscle and a skeletal system of sturdy well-proportioned bones, along with all of the internal systems, connected to produce smooth and directed movement. Please join us as we embark on a wonderful journey exploring the Bull Terrier anatomy.
Your dog’s brain is a sophisticated organ – it controls his thinking, learning, and actions. It’s also responsible for interpreting and integrating information from all over the body, much like our human brains. And, in February 2014, research led by Dr. Attila Andics revealed more similarities.
The study made by the University of Budapest revealed that a dog’s brain reacts to voices in the same way as a human brain. Eleven dogs and owners where each placed in an MRI scanner and played over 200 different sounds – from car sounds and whistles to human sounds and dog noises. The researchers found that a similar region – the temporal pole, which is the most anterior part of the temporal lobe, was activated when both the animals and people heard human voices. “We do know there are voice areas in humans, areas that respond more strongly to human sounds that any other types of sounds,” Dr. Andics explained. “The location (of the activity) in the dog brain is very similar to where we found it in the human brain. The fact that we found these areas exist at all in the dog brain at all is a surprise – it is the first time we have seen this in a non-primate.” The fact that emotionally charged sounds, such as crying or laughter prompted similar responses to humans as it did with the dogs tested might also perhaps explain why dogs are attuned to human emotions.
The size and weight of the brain varies greatly from species; the weight of the brain in an average dog is less than half of one percent of its body weight – but it receives over twenty per cent of the blood pumped out of the heart. So, this shows how the brain is at the core of your dog’s activity, busy digesting data and determining the best course of action, which affects your pooch’s overall behaviour.
The brain is a mass of nerve tissue which is divided up into three main areas; the cerebrum, the cerebellum and the brain stem. Each part performs particular functions with information being fed into these key areas, so collectively they give instructions on the appropriate action.
The cerebrum or cerebral cortex forms the bulk of the brain. This is responsible for receiving and analysing sensory information such as vision, hearing, touch, taste and pain. The larger the cerebral cortex in an animal, the more options of responses it has, enabling it to carry out complex behaviour patterns. For example; reptiles’ cerebral cortex is far less developed compared to your dog’s brain. This means, Fido can perform many tasks and has complex behaviour patterns compared to the reptile.
The cerebral cortex is divided up into two areas; the left and right cerebral hemispheres. The narrow slit separating these hemispheres is called the cerebral longitudinal fissure. Within these two areas are four lobes; the frontal, temporal, parietal and occipital lobe. The frontal and temporal lobes contribute to the alertness, intelligence (planning and execution of movements), memory and temperament of the dog. Within this area is the thalamus. This is responsible for relaying sensory information such as hearing, sight, touch and pain. The thalamus also enables your dog to selectively concentrate and focus on one thing at a time. The sensory and emotional information relayed to the thalamus is then sent to the parietal and occipital lobes of the dog’s brain for decoding. Once this information has been digested and processed according to previous experiences or memories, the data is then sent to the frontal lobe and translated into plans and actions. The thalamus also contributes to the monitoring and regulation of motor activity initiated in the cerebral cortex. This information is then sent from the cerebral cortex to the cerebellum to aid the co-coordinating centre of the brain which is responsible for muscle activity.
Just below the thalamus is the hypothalamus. This area controls the release of the pituitary hormones (from the pituitary gland) and is responsible for regulating your pet’s drinking and eating behaviour, as well as his body temperature, reproductive and autonomic nervous system; this system contains nerves which control involuntary movements of organs such as the intestines, heart, blood vessels and blood (dogs do not have voluntary control over the autonomic nervous system). Interestingly, emotions such as rage and aggression originate in the hypothalamus – although these are normally inhibited by the hippocampus and the frontal lobe of the cerebral cortex – if a dog contracts the rabies virus, this invades the hippocampus and removes this inhibition. This means the powerful aggressive urges of the hypothalamus are allowed to prevail. As you can see, your dog’s brain is a complex machine, and within the cerebral cortex is the limbic system – this regulates the dog’s emotions from fear, rage, and aggression to anxiety, joy and euphoria. It has an essential role in the learning process. The rabies virus will attack the limbic system and this demonstrates how any disturbances in this area can cause emotional and or behavioural problems.
Within the limbic system is the amygdala, this is responsible for survival strategies and defense responses. In times of extreme danger or a life and death situation a dog has to act quickly. So, in this instance the information of this situation is sent directly from the thalamus to the amygdala activating your dog’s defence reactions at speed, rather than it being decoded first by the cerebral cortex which takes longer to process.
The second area of your dog’s brain is the cerebellum (meaning ‘little brain’ in Latin). This is located at the back of the brain and is attached to the brain stem and cerebral cortex. The cerebellum is the part of the brain that regulates or is mostly responsible for the control and co-ordination of voluntary movement (muscles) and posture of your dog. The cerebellum is interconnected via thalamic relays with the sensory-motor area of the cerebral cortex. So, the cerebellum will receive information from the cerebral cortex about intended muscle activity and it will process and compare this information from receptors in your dog’s muscles and tendons. Once the cerebellum has feedback the data, this ensures precision in movement. Any damage or cerebellar lesioning to this area will typically cause head or body tremors, poor balance, signs of clumsiness, exaggerated and awkward movements. The cerebellum, which is responsible for co-ordinated movement and the rest of the nervous system, is not fully developed at birth. While the brain, spinal cord and associated nerves are all present, the nerves lack the ability to efficiently transmit electrical impulses. Most people who have seen a new born puppy will notice how they are sluggish in movement and its pain sensation is very slow.
The third area of the brain is the brain stem. This is located at the base of the brain and is connected to the spinal cord and cerebellum. There are two main parts of the brain stem; the pons and the medulla oblongata. All the nerve fibres leaving the brain going to your dog’s muscles, will pass through the brain stem. The medulla oblongata is situated at the base of the brain and connects to the spinal cord. It’s responsible for regulating a number of functions from your dog’s heart beat and his breathing to salivation, coughing, sneezing and his gastrointestinal functions. The medulla oblongata, together with the pons, is an important relay site for hearing and balance information, taste sensations and motor reactions. The pons provides a pathway for the nerves fibres to relay sensory information between the cerebellum and cerebral cortex. The pons also includes the micturition centre (urination). Studies in 1964 by Japanese scientists Kuru and Yamamoto, demonstrated how electrical stimulation to the pons resulted in an increase in urethral sphincter activity and the relaxation of the bladder. So, it’s safe to assume that damage to the pons will contribute to urinary incontinence.
The central nervous system is comprised of the brain and spinal cord, but connected to these are a network of peripheral nerves (the peripheralnervous system) which penetrate and supply the tissues of the body and transmit pieces of information – such as pain sensation – to and from the body back to the nervous system. In turn, the brain reacts with a course of action. The brain cells that transmit information within the central nervous system are called neurones. Structurally a neuron is unlike any other cell in the body, made up of three parts; the cell body, an axon and dendrites.
The cell body is the large central portion of the cell containing the nucleus and is between the axon and dendrites. The axon is a slender tube that carries nerve impulses away from the neuron to the terminal buttons. Dendrites are short and tree-like; they receive messages from the other neurons. Between the axon terminal button of one cell (presynaptic cell) and the dendrites of the second or receiving cell (postsynaptic cell) is a junction called the synapse. The axon and dendrite in the two cells face each other and the synapse is the very small gap in between. When the information (referred to as the action potential) is being sent through the neurons, the axon terminal of the sending cell triggers the release of a chemical (neurotransmitter) in the immediate area of the dendrite of the receiving cell. Chemicals secreted include; dopamine, noradrenalin and serotonin. And, it is these three neurotransmitters that are important in the treatment of canine behaviour problems. That’s because neurotransmitters can excite, inhibit or alter the activity of other neurons.
Trainer Val Strong uses an analogy that helps us understand how neurotransmitters can excite or inhibit cells. She refers to the receptors on the receiving cell’s membrane like ‘locked doors’. Excitatory neurotransmitters act like keys which open the ‘doors’ allowing information to be passed along the axon of the cell, causing the release of the second cell’s chemical (or neurotransmitter). Whereas inhibitory neurotransmitters acts as ‘bolts’, bolting the receptor doors so the action from the excitatory transmitters have no effect. Changes to the responses of synapses are believed to be the key to memory and learning.
As you can see, your dog’s brain is a powerful organ that’s super sophisicated – enabling him to learn, express emotions and allows for behaviour – helping him to respond and adapt to his environment. So, there’s an awful lot going on ‘up top’!
Reproduction and/or distribution of these materials are prohibited without the express written authorization of Grice, H. (2014) The canine brain, Hanne Grice Pet Training & Behaviour. Available at: https://www.hannegrice.com/physiology/the-canine-brain/ (Accessed: 20 January 2024)
The heart has four chambers. The right atrium (RA) collects venous blood from the body, and it passes through the tricuspid valve to the right ventricle (RV) The right ventricle pumps the venous blood, though the pulmonic valve, into the pulmonary artery and so into the lungs, where the blood is oxygenated. The blood returns to the heart, into the left atrium (LA) Blood passes though the open mitral valve into the main pumping chamber of the heart, the left ventricle (LV) When this pumps, the mitral valve closes and blood is ejected out via the open aortic valve into the aorta which divides to every artery to all the organs of the body.
By Sandra P. Tou , DVM, DACVIM-Cardiology, DACVIM-SAIM, Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Reviewed/Revised Jan 2020 | Modified Oct 2022 Circulatory System - MSD Veterinary Manual
The dog's ear is a complex structure. It is divided into three parts: the outer ear, middle ear, and inner ear.
Outer Ear
Ear Flap (Pinna): The visible, fleshy part of the ear that collects sound.
Ear Canal (External Auditory Canal): Extends from the ear flap to the eardrum, leading to the middle ear.
Middle Ear
Eardrum (Tympanic Membrane): Separates the outer and middle ear; it vibrates in response to sound waves.
Ossicles (Bones): Transmit vibrations from the eardrum to the inner ear.
Inner Ear
Cochlea: Converts vibrations into nerve impulses for hearing.
Vestibular System: Responsible for balance and spatial orientation.
The old adage, “No Hoof, No Horse,” common in North America in the 18th century, speaks to how important the feet are to an animal. A lame horse is useless to its owner. The same principle can be applied to the dog as “No Foot, No Dog.”
The first time I heard the phrase used to describe a dog was when I was judging an ARBA show in the late 1990s. A fellow judge (a hound man), whom I greatly admired, chastised me for using a hound with bad feet in the Group. This led to a great discussion and the beginning of a long friendship.
The feet are the foundation on which the dog is “built.” Just as the foundation for a building must be solid, so must the feet of the dog be correct for its breed.
The anatomy of the canine foot is composed of the toenails (claws), toes, toe (digital) pads, the metacarpal pads, the dewclaw, and the carpal pad. (See Figure 1.) The canine foot has four toes, which are functional and contain three bones to form each toe. A fifth toe, called the “dewclaw” when it is not removed, differs from the other four in that it only contains two bones. The feet serve as a base of support for the dog. They serve as a cushion to absorb shock, and they provide traction to start motion and as a brake to stop.
We will start with the toenails or claws, which are at the end of each toe. (See Figure 2.) Composed of keratin, the nails enable the dog to grip the ground and also to scratch (both the ground and themselves) and help maintain a grip on something they are chewing. The average dog has four functional toes (digits) and may be born with a fifth toe called the dewclaw, located on the inner side of the pastern on the front leg. The dewclaw is considered to have lost most or all of its original function. Dewclaws may also be found on the rear legs. Several breeds require dewclaws on some or all of the legs. On the average dog, however, they are usually removed, especially if they have no contact with the ground.
Each of the toes is supported by a pad composed of thick layers of fat and connective tissue covered with several layers of skin, forming a thick, horny skin. This thick skin makes it possible for the dog to comfortably work over many types of terrain, from abrasive to slick and slippery. It also varies greatly in fluctuating temperatures. The pads serve as a weight bearing, shock absorbing cushion, and aid in traction. (See Figures 1 & 2.)
In the front feet, next comes the metacarpal bones, commonly referred to as the pastern. These bones serve to join the pastern joint(carpus joint) with the toes (digits) of the dog. There are four metacarpal bones (five if the dewclaw is not removed), each leading to one of the toes. Of the four, the outer bones (leading to the two outside toes) are shorter than the two inner bones (leading to the two center toes). These metacarpal bones relate to the palm of the human hand—between the wrist and the fingers. The dog actually walks only on the toes/digits of its foot. (See Figure 2.)
The carpal pads are found on the front feet, farther up the foot near the wrist or pastern joint. (See Figures 1 & 2.) They are of the same structure as the pads under the toes. The carpal pad comes into play on steep or slippery surfaces by helping the dog to retain its balance, It is also sometimes referred to as the “stopper pad,” working as a brake. This pad also serves to support the crouching/crawling dog (think Border Collieapproaching livestock) as it moves over rough terrain.
The metacarpal pads on the front feet (metatarsal on rear) are the largest pads on the foot and are located behind the pads of the toes. As with the toe pads, the metacarpal/metatarsal pads provide shock absorption and traction. The metatarsus of the rear is similar to the metacarpus of the front, except that it is longer. (See Figure 1.)
As we move from the toes, up toward the foreleg, the carpal bones form the pastern joint (wrist). The pastern joint is a compound joint formed by the articulation of the seven carpal bones (stacked in two rows), with the radius and ulna bones of the foreleg on the upper side of the pastern, and the metacarpal bones on the lower side.
These seven bones form a compound joint that allows for a great deal of mobility and has a significant shock-absorbing capacity. This joint allows for the slope of the pastern and provides cushioning for the striking foot. The short bones of the carpus serve to diffuse concussion in the limbs as the bones experience pounding force when a dog runs or lands from a jump. (See Figure 2.) The tarsus, or hock joint on the rear legs, is similar to the pastern on the forelegs as it consists of seven bones arranged in two rows (three on top to articulate with the fibula and tibia bones, and four distal that articulate with the metatarsals of the rear foot).
Foot conformation is directly related to the task the breed was developed to accomplish. A Cat Foot is compact, small, and round in shape. It is built for stability, endurance, and bearing great weight. The compact foot is easily picked up during forward movement, allowing a dog to conserve energy. The cat foot works well for dogs that have to move over uneven ground. Not surprisingly, it is found on most large Working breeds like the Doberman Pinscher and the Newfoundland(See Figure 3.)
The Hare Foot has two elongated middle toes, and is formed for speed and quick changes of direction as well as for fast movement from a standstill. Dog breeds with hare feet include the Whippet and the Greyhound. The longer hare foot allows the foot to get a better grip on the ground when running straight ahead. (See figure 4.)
Dogs with oval feet have slightly longer middle toes (shorter than the hare foot and longer than the cat foot) and are for the dog that must be able to endure, but also needs the added speed and jumping ability associated with the hare foot. The oval foot is found in breeds as diverse as the Pembroke Welsh Corgi, Basenji, Pointer, Chinook, and Toy Fox Terrier. (See Figure 5.)
Dogs with webbed feet increase the surface area of the foot while also providing better movement through water, mud or snow. In breeds such as the Chesapeake Bay Retriever and the Otterhound, as well as the Portuguese Water Dog and the Newfoundland, the webbed foot also serves somewhat as a paddle when swimming. A few breeds even call for “snowshoe” feet, to help the dog traverse more easily on snow and ice. The Alaskan Malamute and the Tibetan Terrier ask for snowshoe feet.
Two types of feet that are considered faulty are the flat foot and the splayed foot. The flat foot is usually accompanied by a dog that is “down in pastern” and is basically due to a laxity of the tendons of the foot and carpal joint. (See Figure 6.) A splayed foot is weak and the toes are spread apart, especially when in motion. (See Figure 7.)
Foot shape can be affected by heredity, lack of exercise during critical periods of development, and improper ground surface during periods of growth. As a breeder, one must always know not only the virtues of the dog we wish to breed, but most importantly, we must also know their faults. We must breed for the whole dog, trying to find a mate that excels where our dog may be faulty, in hope of correcting the faulty parts in the next generation. Again, we must look at the dog as a whole. We must know the traits that are essential to breed type and know where we can “give” a little without losing breed character.
The feet of any breed serve as the foundation upon which the entire dog is “built.” Just as a contractor would never try to construct a building upon a faulty foundation, neither should we ignore the correct foot for our breed. A faulty foundation will eventually fail, and if it does, the entire building is in danger of collapse. As breeders, we should pay very close attention to breeding for the correct foot for our breed, as this is the very foundation upon which our breeds stand. (reprinted from Showsight Magazine)
The integumentary system is the body’s outer layer. It consists of the skin, hair, glands and nails. These organs and structures are the first line of defense against bacteria and help protect from injury and sunlight. The integumentary system works with other systems in the body to keep it in balance. This anatomy section will cover the coat and the nerve supply to the skin, illustrating receptor morphology.
The coat serves as a physical barrier to temperature extremes, UVR (ultraviolet radiation) and minor trauma. The hair coat also sheds water as a result of the lipids provided by sebaceous gland secretion. Tactile hairs and sensory neurons provide awareness of the physical environment, allowing the animal to make appropriate reactions for survival, such as reflex responses to heat and noxious stimuli. It also serves as a warning system. The hair rising on the back usually indicates that the dog is threatened or frightened. The arrector pili muscles, also known as hair erector muscles, are small muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end, known colloquially as goose bumps. This may occur in cold temperatures or, as previously stated, in times of fear.
Some of the differences that occur in the appearance of the coat of various types of dogs are due to the variation in the implantation angle of the hair follicles. Studies have shown that the majority of all breeds have an angle of 30 to 40 degrees.
The hair follicles are compound, which means the follicles have a central hair surrounded by 3 to 15 smaller secondary hairs all exiting from one pore. Dogs are born with simple hair follicles that develop into compound hair follicles. Accessory hairs develop as the puppy gets close to 3 months old, at which time there are two to five secondary hairs around each primary hair. At 6 months there are five to fifteen hairs in each follicle bundle, further grouped in clusters of three in irregular rows, and 100 to 300 bundles per square centimeter. So, that’s about 4,500 hairs per square centimeter. If you’re measuring in inches that’s approximately 11,000 hairs per square inch. The growth of the hair is affected by nutrition, hormones and change of the season.
And, we must not forget to mention the third type of hair on our Bull Terriers, the whiskers! Dogs have keen senses of smell and of hearing but their weakest sense is their vision, especially their near vision. This is where the whiskers come into play. A whisker’s purpose is all about helping a dog navigate the world. The whiskers, otherwise known as vibrissae, are coarser and thicker than regular hair and have roots that are three times deeper. They are commonly located just below the nose on both the left & right side (Mystacial Vibrissae), the chin (Chin Vibrissae), on the lower jaw (Mandibular Vibrissae), on the cheeks (Zygomatic Vibrissae), and above the eyes (Superciliary Vibrissae). Another purpose of the whiskers has to do with communication, in the form of emotional response. Dogs who are scared or feel threatened often have flared whiskers. Sleeping dogs often have whiskers that lie flat. Dogs that are sniffing their surroundings with curiosity will have whiskers protruding out toward the source of the smell.
Whiskers are more sensitive than regular hairs because the follicles from which they originate are packed with blood vessels and nerves. In fact, a dog’s whiskers are as sensitive as a human’s fingertips. They don’t actually feel anything, they transmit information to sensory cells when they detect objects or movement. As a dog approaches something in his path, he stirs up air currents that bounce back when they hit solid objects. Whiskers detect very faint vibrations caused by these changes in air currents. These sensitive hairs respond when touched by the smallest particles. When a speck of dust falls on a whisker above his eye, a dog will blink or shake his head and fling it off. This reaction protects the eye which can be injured by even tiny dust particles.
A good portion of a dog’s brain is devoted to processing data from touch sensors. Almost 40% of the brain’s sensory area aligns with parts of the body that have whiskers. Each individual whisker can be traced back to a specific spot in the brain which means that whiskers occupy valuable neurological space in a dog’s body.
Trimming can affect the whisker’s ability to function properly, making the dog slightly less spatially aware. The dog may not get enough information from their environment to move easily. They may become uncertain and move around more slowly in dim lighting. Trimming doesn’t cause your dog pain but if you were to pluck them, which you should never do, they would feel a lot of pain. The whiskers will grow back, as long as the follicle isn’t damaged. It can take two to three months for them to grow back to their original length, depending on how much was trimmed off. It’s best to just leave the whiskers alone. If the whiskers get muddy, gently wipe them off with a damp cloth.
Dogs shedding whiskers are as common as humans shedding skin. Dog whiskers will naturally break, splinter, or fall out. Dogs will still be able to function normally when they shed whiskers naturally. If your dog suddenly starts shedding whiskers faster than they can replace them, it can be cause for concern. They could become confused, and disoriented, and it could signify an underlying health problem.
Our Bull Terriers are fascinating animals and possess amazing capabilities many aren’t even aware of!
Meissner’s Corpuscles consist of a cutaneous nerve ending responsible for transmitting the sensations of fine, discriminative touch & vibration.
Free Nerve Endings can detect temperature, mechanical stimuli (touch, pressure, stretch) & chemical signals and alert the body of potential dangers.
Tactile Disks is are oval sense organs made of flattened cells and encapsulated nerve endings. They have high tactile acuity for an object’s physical features, such as texture, shape and edges. They are abundant in the area of whisker hair follicles of mammals.
Sebaceous Glands secrete an oily substance called sebum. They are present in large numbers near the paws, back of the neck, rump, chin, and tail area. Sebum is a mixture of fatty acid and is important for keeping the skin soft, moist and pliable.
Krause end bulbs are nerve endings located in the skin that are sensitive to touch. They are composed of sensory cells that are connected to a nerve bundle and are responsible for detecting different types of touch, including light and heavy touch, vibration and temperature.
Pacinian Corpuscles are sensory receptors for vibration and deep pressure. They can be found in the whole body; however, the foot pad is where they occur most numerously and tightly grouped.
Nerve Endings around Hair Follicles - At the base of the hair follicle are sensory nerve fibers that wrap around each hair bulb. One of the main functions of hair is to act as a sensitive touch receptor.
Ruffini Endings are slowly adapting encapsulated receptors that detect skin stretch, joint activity and warmth.
Sweat Glands – There are two basic types of sweat glands: apocrine sweat glands and merocrine (also called eccrine) sweat glands. Both produce a very small amount of sweat, which isn’t very effective for body cooling. Apocrine glands are located throughout haired areas of the skin and produce only a scent. These ducts open in the superficial portion of the hair follicle and do not aid in cooling. Eccrine glands, in contrast to apocrine glands, have ducts that open directly onto the surface of the epidermis. These glands are confined mainly to the nose and pawpads. They produce only a tiny amount of sweat.
The tail gland, also referred to as the violet gland or supracaudal gland, area is an oval-shaped area, 2.5 to 4 cm. long, and located on the dorsal aspect of the tail above the 7th to 9th caudal vertebrae.
The hairs of this area are larger, very stiff and coarse. They emerge from the hair follicles singly. The surrounding hair is of the complex follicle type, supporting 6 to 11 hairs. The skin in this area may have a waxy appearance due to an abundance of sebaceous secretions. The apocrine glands (scent glands involved in production of pheromones) and the sebaceous glands of the area are large, extending deep into the dermis and subcutaneous tissue.
The tail gland’s main purpose is to secrete substances that create odors that are used for scent marking and to support olfactory signaling. The secretions are similar to those produced by violets, hence the name violet gland. The chemicals are produced in much greater quantity than in flowers, resulting in a strong smell that can be quite unpleasant. It is often described as a musky or rancid smell and is, most likely, a result of sebum or bacteria on the skin.
Sometimes the hair over this gland tends to fall out when androgen (hormones that contribute to growth and reproduction in both sexes) levels are high over a prolonged period of time. For some Bull Terriers the usually inconspicuous gland area may appear as a noticeably sparsely-haired patch. This condition is sometimes referred to as “stud tail”. Extensive studies have revealed a definite dimorphism of this gland in both sexes resulting in the conclusion that it is an organ associated with estrus.
Surface contour, hair arrangement, & histology of tail gland area. (After Lovell and Getty 1957)
