Feline Skeletal Similarities From Head to Tail

It’s been awhile since we discussed the differences in the skulls of the Pantherinae subfamily, but what about the similarities that are shared amongst all the members of the Felinae family?

We’ll start with the same topic as the last feline post, skulls!

catfront
http://academic.emporia.edu/sievertl/verstruc/catskull.htm

Comprised of seven bones that eventually fuse together as the feline matures, the skull is divided into the front and back. The three front bones of the skull form the zygoma. The zygoma, in particular, influences ear placement to some degree. But, all of the skull bones form an attachment for the muscles which control the ears, jaw, and neck.

The zygoma consists of three portions: the frontal, malar, and lacrimal.

The frontal forms the forehead and front of the skull, ending just where the upper form of the eye socket is located. Its main function is to protect the brain.

Next comes the malar, the lateral projection of the skull known as the check bone. Its purpose is to protect and enclose the eye as well as providing an increased surface area for the muscle attachment to operate the jaws. In longer heads, the arch is not as curved (less marked), causing the malar portion to be much straighter. This results in the oblique or slanted eyes in cat breeds such as the Turkish Angora or the Abyssinian. In rounder heads, more curve in the cheeks is needed to provide for proper bone alignment. A curved arch also provides an orbit, or eye socket, curved enough to form the large, round eyes known for breeds like the British Shorthair.

Last, but not least, is the lacrimal. Located between the cheek bones, the lacrimal is related to the ear ducks. This portion of the skull is small, containing a groove or canal which carries the tear duct from the orbit to the nasal cavity. For cats with normal or long heads, the lacrimal is generally positioned properly. However, for breeds with foreshortened faces, improper breeding can cause the lacrimal to be pushed into misalignment. The alter causes the lacrimal to push up against the eyeball, putting pressure on the tear duct, creating excessive “tearing” or “running” of the eyes.

With that, the zygoma attaches with the two maxillary bones that form the upper jaw and roof of the mouth. These two bones are also part of the nasal cavity and sinuses.

lionskull3
A lion skull showing the nasal cavity and foramen

Within the nasal cavity is porous tissues (olfactory epithelium) covering the turbinate bones, two bilateral spongy curled bones protruding into the nasal passages. These unusual structures warm, clean, and humidify air that is inhaled. They also cool down air exhaled from the lungs, where it has picked up more heat and moisture, to reclaim moisture and prevent dehydration. In humans, when we have allergic reactions, the epithelium is what gets swollen and obstructs our breathing.

This turbinate system benefits the sense of smell. Humidifying the incoming air preserves the delicate olfactory epithelium, keeping the olfactory receptors “healthy” and “alert”. The turbinates also increase the surface area inside the nose and direct air upward toward the olfactory receptors. Compared to dogs, cats possess a much smaller and less developed set of nasal turbinates.

In the maxillary bone, right under both orbits, are openings flanking the nasal cavity. Known as the infraorbital foramen, the two openings are passageways into the eye area for the infraorbital nerve, artery, and vein.

Typically, the foramen is a single opening but with Asiatic lion skulls, the infraorbital foramina is divided, with a bony bridge across the opening. Some researchers hypothesized that this variation amongst the Asiatic lions is due to a severe population bottleneck at some point in the recent past.

The upper jaw is then connected with the lower jaw, or the mandible, which also partially connects with the cheek bone, or the malar portion of the skull. Improper alignment of the upper and lower jaws lead to a bad bite or cleft palate.

Aside from the skull, the overall skeletal structure is similar in all felines and accounting for the size difference and bipedal abilities, the skeletons of the cat and the human is pretty similar. The key differences are meant for the speed, power, and flexibility that cats are known for.

Cats are digitigrades, meaning that they walk on their toes (similar to walking in ballet shoes). As hunters, they need speed to catch their prey. Using digitigrade locomotion, felines are able to lengthen their limbs, therefore their stride. Because they walk on their toes, only a small area of the foot touches the ground, accelerating movement.

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Drawing By: Cheesy Game Art (@Tumblr)

Unlike most mammals, cats have a “pacing” gait; that is, moving two legs on one side of the body before the legs on the other side. Other mammals that share this trait are camels and giraffes. As the cat speeds up, the gait will change to a “diagonal” gait, which is similar to most other mammals, where the opposite hind and forelegs move simultaneously.

All felines directly register, placing each hind paw almost directly in the print of the corresponding forepaw, when walking. This minimizes noise and visible tracks as well as provides sure footing when they navigate rough terrain.

Another characteristic of a hunter is power. For cats, their power is found in their hind limbs. Longer than their forelimbs, the hind limbs are important for acceleration and jumping.

Unlike the rest of the feline body, its forelimbs sacrificed mobility and flexibility for power. The stifle (knee), hock (ankle), and foot cannot move sideways. But, the sturdy bones and toned muscles allows for strong and quick propulsion.

Finally, the feline’s grace and flexibility is attributed to its flexible spine and a reduced clavicle, which is found in many hoofed and carnivorous mammals.

The vertebrae in the cat’s vertebral column are much more loosely connected to each other than in humans. Because of this, the degree of movement between the individual vertebrae is smaller than in humans. However, compared to many other animals, these bones are still much less tightly connected.

At the top of the vertebral column, in the neck and cervical region, the first two vertebrae (named atlas and axis) are shaped to enable the head to make a wider range of movement.

The same can be said for the long, pliant tail that acts like a rudder to improve balance required during the hunting process.

 cat-righting-reflexNot only does it allow for movement, but the flexible spine also allows for rotation along  the length of the spine due to the smooth and round articulations of the vertebrae. It allows the cat to “coil” or compress the spine to spring or leap high, arch the back into an inverted ‘U’ shape, bend itself in half, or rotate the rotate the front end of the body 180 degrees relative to the back. Along with the brain’s balancing mechanisms, the supple back allows the cat to turn right side up, landing on its feet in less than two seconds.

Along with the flexible spine, the greatly reduced collar bones, or clavicles, of the shoulder girdle allows for freer movement of the front legs. The clavicles stabilize and give strength to the shoulder joints, thus enabling humans to lift heavy objects with the forearms.

However, cats do not require such strength, instead they need maximum speed. The undeveloped or absent clavicles liberate the shoulder blades to move with the corresponding front legs freely with being attached to the shoulder joints. This increases the feline’s efficiency and speed of motion between the shoulder blades and front legs, lengthening the stride. Since running speed is equal to the stride length times stride frequency (number of strides per unit of time), a longer stride length allows the cat to run faster without having to move its limbs so quickly.

Other than increasing the stride, it also allows for the mobility required to catch prey in any direction as well as narrowing the cat’s chest, providing further speed, flexibility, and ability to squeeze through tight openings.

Outside of these key differences that make up the feline, the formation of bones is a similar process that is found in many other vertebrates.

There are two types of bones: cartilage and membrane. Cartilage develops late in the embryo stage before the kitten is born. Later on, the cartilage provides a model for the shape of the bone, which forms on the surface. Membrane bones develop directly without having the cartilage layer. Some face, skull, and front end bones are formed in this manner.

Bones are constantly being renewed through bone growth and resorption, the removal of the bone by dissolution and degradation. The rates at which this process occurs changes as the cat matures and are also affected by disease, malnutrition, or accidents.

feline-anatomy-skeleton

As spongy bone is formed, it encloses an area of vascular tissue. As the bones increase in size, the original interior or the older parts of the bone are resorbed  to increase the size of the inner cavity. With a new deposit of new bone on the external surface, they will continue to grow in circumference. Bones will get thinner and weaker as the amount of new bone is less than that of being dissolved due to the inability to absorb dietary calcium.

Feather or porous bone are extremely detrimental for cats. These bones are easy to feel. If one picks up a large cat and seems to “flout out” of one’s hands or feels for the circumference of the bone and is not proportion to the feline’s size, than the cat has porous bones. The light bones do not provide the framework enough strength to support the muscles and tendons, leading to a breakdown of bone assemblies and causing an imbalance.

While the skeleton remains similar throughout all felines, despite the size, environmental pressure create some natural variations in shape. Hot-climate cats are typically smaller with a higher surface to weight ratio to aid in cooling. Cold-climate cats tend to have larger, sturdier skeletons with thick coats.

Human interference has also caused changes in the the skeletons of certain breeds. Breeds like the siamese and orientals have been bred to have much thinner leg bones while the british shorthair is being bred to have a much heavier and more compact skeleton than most other cats.

References + For More Reading

Views of a Lion Skull

Floating Forelimbs and Clavicles

Motor Patterns in Walking

Skeleton of a Cat

Cats (Eyewitness Companions) by Dr. Bruce Fogle

Pieces of a Cat by Carol V Brown

Feline Anatomy

For Others in the Series

Pantherinae Skull and Larynx Comparison

The Feline Skeletal Anatomy

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