Flashcards: the dog's skeleton

cranium · skull

The skull protects the brain and the sense organs and forms the face: the orbits in which the eyes sit, the nasal cavity with the turbinates and the maxilla with the upper teeth. It is made of several bones joined by sutures. The mandible articulates with the temporal bone at the temporomandibular joint.

Where: The bones of the head, without the mandible.

mandibula · mandible

The mandible is the bone of the lower jaw. It carries the lower teeth and articulates with the temporal bone of the skull at the temporomandibular joint, the one that allows the mouth to open and close. Its length relative to the maxilla determines how the lower teeth sit against the upper ones, that is, the occlusion.

Where: The bone of the lower jaw, articulated with the skull at the temporomandibular joint.

vertebrae cervicales · cervical vertebrae

The cervical spine has seven vertebrae, in all breeds, from the Chihuahua to the Great Dane. The first two, the atlas and the axis, have special shapes and allow the "yes" and "no" movements of the head. The cervical vertebrae carry the head and are the attachment point of the neck muscles.

Where: The vertebral column in the neck region.

vertebrae thoracicae · thoracic vertebrae

The thirteen thoracic vertebrae each carry a pair of ribs. Their spinous processes, the upward projections, are tallest at the first vertebrae and form the withers together with the edges of the scapulae. Toward the rear, the processes get shorter and the back becomes more flexible.

Where: The vertebral column above the thorax, from the withers to the last rib.

vertebrae lumbales · lumbar vertebrae

The seven lumbar vertebrae are the largest vertebrae of the spine and have no ribs. Their wide transverse processes anchor the powerful muscles of the back. The number sometimes varies: in a study of 89 dogs, about 4.5% had an extra lumbar vertebra or a transitional one.

Where: The vertebral column between the last rib and the sacrum.

os sacrum · sacrum

The sacrum is made of the three sacral vertebrae, fused into a single bone. The pelvis attaches to it through the sacroiliac joint: this is the bony link through which the force of the hindlimbs reaches the spine and pushes the body forward. The sacrum continues with the tail vertebrae.

Where: Between the lumbar vertebrae and the tail, under the croup.

vertebrae caudales · caudal vertebrae

The caudal vertebrae form the skeleton of the tail: usually between twenty and twenty-three, getting smaller toward the tip, where they become simple bony nodules. The number differs between dogs. The first tail vertebrae still have processes and a vertebral canal; the last ones are just vertebral bodies.

Where: The skeleton of the tail.

costae · ribs

The dog has thirteen pairs of ribs: nine sternal, which reach the sternum through their cartilage, and four asternal, whose cartilages join each other and form the costal arch. The last pair is usually "floating", free at its lower end. The ribs protect the heart and lungs.

Where: From the thoracic vertebrae to the sternum, on the sides of the thorax.

sternum · sternum

The sternum is the bone on the bottom line of the chest. In the dog it is made of eight sternebrae, bony segments joined by cartilage, which remain separate throughout life. The front end, the manubrium, can be felt at the forechest; the rear end, the xiphoid process, sits at the start of the abdomen.

Where: On the bottom line of the thorax, between the two rows of ribs.

scapula · scapula, shoulder blade

The scapula is the flat, triangular bone of the shoulder. It has no joint with the trunk: in the dog the clavicle is a rudiment of about one centimeter, not connected to the skeleton, so the forelimb "hangs" from the body in a sling of muscles and ligaments. With the humerus it forms the shoulder joint.

Where: The flat bone on the side of the thorax, under the shoulder region.

humerus · humerus

The humerus is the bone of the upper arm. Its round head articulates with the scapula at the shoulder, and its lower end with the radius and ulna at the elbow. In the standing dog it slopes backward, which is why the elbow comes under the thorax, not under the shoulder. It is one of the strongest bones of the forelimb.

Where: The bone of the upper arm, from the shoulder to the elbow.

radius · radius

The radius is the front bone of the forearm and the one that carries most of the weight between the elbow and the carpus. It articulates with the humerus above and with the carpal bones below. Together with the ulna it forms a pair of bones lying side by side, with little rotation between them.

Where: The front bone of the forearm, from the elbow to the carpus.

ulna · ulna

The ulna is the second bone of the forearm. It sits behind the radius at the elbow and on the outer side at the carpus. Its upper end, the olecranon, is the bump we call the point of the elbow; the tendon of the triceps muscle, the one that extends the elbow at every stride, attaches to it.

Where: The rear bone of the forearm; its upper end is the point of the elbow.

ossa carpi · carpal bones

The dog's carpus has seven small bones, in two rows, between the forearm and the metacarpus. There are seven, not eight as in other species, because the radial and intermediate bones are fused. The carpal joint corresponds to the human wrist and bends a long way backward.

Where: Between the radius/ulna and the metacarpus.

ossa metacarpalia · metacarpus

The metacarpal bones link the carpus to the toes. Since the dog is digitigrade, the metacarpus stands raised off the ground, nearly vertical, and the weight passes through the toes and pads. Metacarpal I, that of the dewclaw, is much shorter than the others and does not reach the ground.

Where: Between the carpus and the front toes; the segment of the paw raised off the ground.

digiti manus · digits (forepaw)

The digits are numbered I to V, from the inside outward. Digits II-V touch the ground, each with three phalanges, a pad and a claw. Digit I, the dewclaw, is slender, sits higher on the inner side of the paw and takes no part in support; in some puppies it is removed at birth.

Where: The end of the forepaw, with the pads and claws.

os coxae · pelvis, os coxae

The pelvis is formed by the two hip bones, each made of the ilium, ischium and pubis, which meet at the acetabulum, the socket into which the head of the femur fits. The pelvis attaches firmly to the sacrum through the sacroiliac joint; the rear end of the ischium is the "point of the buttock", a landmark for body length.

Where: Under the croup, between the sacrum and the femur.

femur · femur

The femur is the bone of the thigh. Its round head fits into the acetabulum of the pelvis, at the hip; its lower end articulates with the tibia and the patella, at the stifle. In the standing dog it slopes forward, which is why the stifle comes forward, close to the line of the abdomen.

Where: The bone of the thigh, from the hip to the stifle.

patella · patella, kneecap

The patella is a small bone in front of the stifle, held in the tendon of the quadriceps. It slides in a groove of the femur when the stifle flexes and extends. The femoropatellar joint is, together with the femorotibial joint, what we call the stifle or knee; you can feel the patella and its ligament under the skin.

Where: In front of the stifle, in the tendon of the quadriceps muscle.

tibia · tibia

The tibia is the large bone of the lower leg. At the top it articulates with the femur at the stifle, at the bottom with the tarsal bones at the hock. It carries almost all the weight that passes through the lower leg; the slender fibula lies alongside it. The slope of the tibia in the standing dog sets the angle of the hock.

Where: The main bone of the lower leg, from the stifle to the hock.

fibula · fibula

The fibula is the slender bone on the outer side of the lower leg, parallel to the tibia. It carries no significant weight; its main role is to give muscles attachment points and to stabilize the hock at its lower end. In the illustration it shows as a narrow line behind the tibia.

Where: The slender bone on the outer side of the lower leg.

ossa tarsi · tarsal bones

The tarsus has seven bones. The largest, the calcaneus, extends upward and backward and forms the point of the hock; the common calcaneal tendon (the “Achilles tendon”) attaches to it. Next to it lies the talus, which articulates with the tibia. The tarsal joint is the counterpart of the human ankle.

Where: Between the tibia/fibula and the metatarsus; they form the hock.

ossa metatarsalia · metatarsus

The metatarsal bones link the tarsus to the hind digits and, like the metacarpus, stand raised off the ground: the dog walks on its toes. Behind them lies the common metatarsal pad. The metatarsus is generally somewhat longer than the metacarpus, which gives the hind limb its pushing “lever”.

Where: Between the tarsus and the hind digits.

digiti pedis · digits (hind paw)

The hind paw usually has four weight-bearing digits, II-V, each with three phalanges, a pad and a claw. Digit I, the hind dewclaw, is absent in most dogs; in some breeds it is present and even required by the standard, sometimes double. The digits take the final push-off at every stride.

Where: The end of the hind paw.

orbita

In the dog the bony rim of the orbit is incomplete laterally: the circle is closed by the orbital ligament, which runs from the zygomatic process of the frontal bone to the zygomatic arch. The orbit holds the eyeball, the seven extraocular muscles of domestic mammals (four recti, two obliques and the retractor) and the gland of the third eyelid.

Where: The bony cavity of the eye.

arcus zygomaticus

Formed by the union of the zygomatic process of the temporal bone with the temporal process of the zygomatic bone. It bounds the temporal fossa laterally, where the temporalis muscle lies, and the masseter arises from its lower edge. In brachycephalic breeds the arches are wide.

Where: The cheekbone, below the eye, from the orbit to the jaw joint; easily felt under the skin.

articulatio temporomandibularis

The joint between the mandibular fossa of the temporal bone and the condylar process of the mandible; it allows the mouth to open and close. The temporalis muscle guards it against forward luxation. It can be felt under the skin, in front of the ear, when the dog opens its mouth.

Where: The jaw joint, below the ear, behind the zygomatic arch.

bulla tympanica

A rounded bony swelling of the tympanic part of the temporal bone, large in carnivores. It encloses the ventral part of the middle ear cavity, with the eardrum and the three ossicles; from here the inner ear begins, with the cochlea and the vestibular labyrinth (hearing and balance).

Where: Under the skull, behind the jaw joint.

protuberantia occipitalis externa

A median prominence at the junction of the interparietal bone with the occipital bone; in the dog and the horse it corresponds to the highest point of the skull. The nuchal crest is its transverse extension. A palpable landmark used when measuring the length of the skull.

Where: The rearmost point of the skull, at the nape; easily felt under the skin.

crista sagittalis externa

Present in carnivores, it varies greatly between breeds; part of the temporalis muscle arises from it. The more developed it is, the more attachment surface there is for the biting muscles.

Where: The ridge along the middle of the skull, between the two temporal fossae, up to the occipital protuberance.

os nasale · nasal bone

The nasal bones, paired, form the upper part of the roof of the nasal cavity. They articulate with each other on the midline, laterally with the maxillae and caudally with the frontal bone. In the dog, in most breeds, they are long and wider in front, their rostral ends form an almost semicircular nasal notch, and their outer surface has a central groove. The front part of the dorsal nasal concha attaches to them.

Where: The roof of the nasal cavity, on the bridge of the nose; paired.

os incisivum · incisive bone (premaxilla)

The incisive bone, or premaxilla, lies at the rostral end of the head and carries the upper incisors. In the dog its body is flattened dorsoventrally, with three alveoli that grow from the first to the third incisor, and it completes the alveolus of the canine. The nasal process forms the lateral edge of the bony nasal opening, the palatine process the front of the hard palate. Behind the incisors open the canals to the vomeronasal organ.

Where: The bony tip of the muzzle; carries the upper incisors.

maxilla · maxilla

The maxilla is the largest bone of the face and carries the upper premolars, molars and canine. In the dog it is short but very tall at the back, without a facial crest; the infraorbital foramen, through which the infraorbital nerve emerges toward the lip and the nose, lies above the third premolar, and the infraorbital canal is short. The ventral nasal concha attaches to its surface facing the nasal cavity.

Where: The facial bone above the upper teeth, in front of the orbit.

os frontale · frontal bone

The frontal bone, paired, forms the base of the forehead region: the nasal and orbital parts belong to the face, the squamous part to the roof of the skull. In the dog, the supraorbital process is very short, so the upper edge of the orbit is incomplete, as in the pig, and is closed by the orbital ligament. The frontal sinus, divided into compartments in the dog, is hollowed out in this bone, above the lateral masses of the ethmoid.

Where: The base of the forehead: above the orbits, between the nasal and the parietal bones.

os parietale · parietal bone

The parietal bones, joined on the midline, form most of the roof of the cranial cavity; they lie above the temporal bone, between the frontal and the occipital bone. In the dog, where the two bones meet, a prominent parietal crest rises and continues onto the frontals: the sagittal crest of the skeleton layer, to which the temporalis muscle attaches.

Where: The roof of the braincase, between the frontal and the occipital bone.

os occipitale · occipital bone

The occipital bone closes the skull at the back and articulates with the first cervical vertebra, the atlas, through its two condyles. In the dog, the basilar part is wide and flat, and the nuchal crest, its peak, projects strongly backward in large breeds: it is the external occipital protuberance you feel at the nape. From it arise the digastricus and part of the muscles of the nape.

Where: The back end of the skull, where the atlas attaches.

os temporale · temporal bone

The temporal bone forms the lateral region of the skull and houses the organs of hearing. Its parts, petrous, tympanic and squamous, fuse early in the dog. The zygomatic process curves widely outward and forms the back part of the zygomatic arch; the external acoustic meatus is wide and very short, and the bony bulla is very large, round and smooth. The mandible articulates on it.

Where: The lateral part of the skull, around the ear, with the tympanic bulla.

os zygomaticum · zygomatic bone

The zygomatic bone, also called the malar, is a flat bone of the face that forms the lateroventral edge of the orbit and the front part of the zygomatic arch; its temporal process joins the zygomatic process of the temporal bone. In the dog, the zygomatic process is very long and strongly curved, and the frontal process, to which the orbital ligament attaches, completes the orbit, which is open laterally in carnivores.

Where: The cheekbone, below the orbit; the front part of the zygomatic arch.

apparatus hyoideus · hyoid apparatus

The hyoid apparatus is a chain of small bones that supports the tongue and the larynx, set in the back of the space between the bodies of the mandible; it attaches dorsally to the styloid processes of the temporal bones, ventrally to the larynx and the root of the tongue. Its pieces: basihyoid, thyrohyoid, ceratohyoid, epihyoid and stylohyoid; in the dog the stylohyoid is slightly longer than the epihyoid. The muscles of the tongue and neck attach to it.

Where: Between the rami of the mandible, attached above to the temporal bone, below to the larynx.