First, let’s start with some quick anatomy. A cat’s tail has 19 to 23 vertebrae, about 10 percent of the total number of bones in its body. An extensive group of muscles, ligaments, and tendons hold the tail together and provide its amazing mobility. Also, the average tail length of a male cat is 11 inches, and for a female it’s 9.9 inches. The tail acts as a counterweight when the cat walks along narrow surfaces like fence tops or chair backs. It also helps a running cat to stay standing as he makes sharp turns in pursuit of prey … or his favorite toy. Cats communicate largely through body language, and the tail is one of the most important parts of your cat’s communication toolbox. By understanding “tail talk,” you can understand how your cat is feeling with just a glance. A happy cat, for instance, walks with his tail held high, and a super-happy cat will add a quiver at the tail tip to demonstrate joy. A mildly annoyed cat will twitch the end of his tail, but if he’s lashing his tail back and forth, you’d better step away, because the claws are about to come out. A cat concentrating on prey will have his tail held low to the ground, although there might be a very slight twitching at the end as he tries to control his excitement. There are a few bobtailed or tailess cats, the American Bobtail or Manx cats are both good examples. Although usually bobtails are the healthier of the two, but a reputable breeder can give you a beautiful healthy Manx that will be with you for years.
Dog eye (Photo credit, deviantart)
Now we are going to look at canine eyes. The socket in which the eye resides is called the orbit, the orbit is a structure that is formed by several bones. It also contains muscles, nerves, blood vessels, and tear ducts. The white of the eye is called the sclera, and is a relatively tough layer covered by a thin membrane. This membrane also covers the cornea, which is the clear dome in the front center of the eye that lets light in. And that brings us to the iris. The iris is the circular, colored area of the eye, it controls the amount of light that enters the eye by making the pupil larger or smaller. When the environment is dark, the pupil enlarges to let in more light; when the environment is bright, the pupil becomes smaller to let in less light. The lens, which sits behind the iris, changes its shape to focus light onto the retina. Small muscles (ciliary muscles) contract to cause the lens to become thicker, which allows the lens to focus on nearby objects. They can also relax to cause the lens to become thinner when it focuses on distant objects. The retina contains the cells that sense light (photoreceptors). These lens changes are limited in dogs. The most sensitive area of the retina is called the area centralis. This area contains thousands of tightly packed photoreceptors that make visual images sharp. Each photoreceptor is attached to a nerve fiber. And all the nerve fibers are bundled together to form the optic nerve. The photoreceptors in the retina convert the image into electrical impulses, which are carried to the brain by the optic nerve. The upper and lower eyelids are thin folds of skin that can cover the eye and reflexively blink to protect the eye.Blinking also helps spread tears over the surface of the eye, keeping it moist and clearing away small particles. The eyes of a dog are protected not only by the same types of eyelids that people have, but also by the nictitating membrane, which is sometimes called the third eyelid. This additional eyelid is a whitish pink color, and is found under the outer eyelids in the inside corner of the eye (near the nose). The third eyelid extends across the eye when needed to protect the eyeball from scratches (for example, while traveling through brush) or in response to inflammation. Most animal’s eyes seem so similar, yet if you really take a look you can see that they’re more than meets the eye. (Sorry I had to)
Chameleon, (Photo credit, somepets.com)
This week, as you probably guessed, I am going to inform you on Chameleon eyes. It is widely believed that chameleons can look in two different directions at the same time, well, this turns out be only partially true. Chameleons can scan their surroundings for danger or prey, but they cannot focus in two different directions. When they hunt, they must look at their prey with both eyes before striking. One thing that the chameleon has going for it are negative lens, meaning that the lens in their eyes are concave. This increases the retinal image size, allowing more precise focusing. In fact, image magnification in chameleons is higher in a scaled comparison than all other vertebrate’s eyes. While the lens is negative, the cornea is positive or convex. This also contributes to precise focusing by improving sight resolution in a narrower field of vision. When you think about it, Chameleons don’t really need long range vision. They usually live in an environment rich with bugs anyway, so they don’t need to look a long ways for their next meal. And let’s face it. They’re too slow to get out of the way of a swooping bird anyway.
To see some lizard with their eyes facing different directions, click here to watch my video.
Cat face (photo credit, photosof.org)
Now I’m going to focus on feline eyes. Cats, like dogs and many other animals, have a tapetum lucidum. Which is a reflective layer behind the retina that sends light passing through the retina back into the eye. While this improves the ability to see in darkness, it appears to reduce net visual acuity, thus detracting when light is abundant. In very bright light, the iris closes to a slit, reducing the amount of light on the sensitive retina, and improving depth perception. The tapetum and other mechanisms give the cat a minimum light detection threshold up to seven times lower than that of humans. Variation in color of cats’ eyes in flash photographs is largely due to the reflection of the flash by the tapetum. Cats have a visual field of view of about 200°, while humans only have 180°. But their binocular field (overlapping the images from each eye) is narrower than that of humans. As with most predators, their eyes face forward, affording depth perception at the expense of field of view. Field of view is largely dependent upon the placement of the eyes, but may also be related to the eye’s construction. Instead of the fovea, which gives humans sharp central vision, cats have a central band known as the visual streak. Cats can see some colors, and can tell the difference between red, blue and yellow lights, as well as between red and green lights. They are also able to distinguish between blues and violets better than between colors near the red end of the spectrum. I’ve noticed a “win some lose some” pattern with different kind of eyes, Humans can’t see well in the dark, cats can’t see all the colors, And chameleons can’t focus on two different things. But that’s for next week.
To see the inside of a cat’s eye, click here to watch my video.
Tarsier (Photo credit, Ricky Garni)
For the next couple weeks I am going to write about a very interesting subject, eyes. First on the list we’ll head to the islands of Southeast Asia to take a look at the world’s only carnivorous primate. The Tarsier. The tarsier is a small animal with enormous eyes. Each eyeball is as large as this creature’s entire brain. The unique cranial anatomy of the tarsier results from the need to balance their large eyes and heavy head so they are able to wait silently for unsuspecting prey. As you may have guessed, the tarsier has very acute eyesight, excellent night vision, and may also be able to see ultraviolet light! The tarsier’s eyes are the largest of any mammal relative to body size. In fact, if a human’s eyes were proportionally as large as those of the tarsier, they would be the size of grapefruits. Its eyes are fixed to its skull and don’t turn in their sockets. Fortunately, it has a very bendable neck and can rotate its head 180 degrees, just like an owl. Not that that makes it any less creepy looking, but on the other hand it sort of looks like my dad so… I guess it’s ok.
To watch my video, click here.
Cat spleen (Photo credit: Wikipedia)
Now we’re going to look at a different kind of organ. The feline spleen. The spleen is an elongated organ located near the stomach in the left forward part of the abdomen. The exact location of the spleen depends upon its size and shape and is affected by the size of the surrounding organs, such as the fullness of the stomach. The spleen is a relatively large, dark red organ that is supplied with numerous blood vessels. A normal spleen is shaped somewhat like a tongue and is considerably longer than it is wide and slightly constricted in the middle. It is also covered by a tough capsule of fibrous tissue. The spleen has a few main functions. Though not essential for life, the spleen does make life a lot easier. Performing important functions like filtering particles in the blood and lymph systems like old or abnormal blood cells and foreign proteins. Acting as a storage site and filtration system for red blood cells and platelets (clotting elements). It is the major site outside the bone marrow where red blood cells are made. And last but not least, the body has the ability to contract the spleen suddenly if additional red blood cells are needed in the bloodstream. So even though it is not essential for life, the spleen sure makes life a lot nicer.
Click here to watch my video
Blobfish (photo credit, SEA SERPENT)
This week I’m going to write about something a little different. Variety is the spice of life you know. So I will be informing you on the blobfish. The blobfish is a deep sea fish of the family Psychrolutidae. It inhabits the deep (and I mean DEEP) waters off the coast of mainland Australia, Tasmania, and New Zealand. They live at depths between 2,000 and 3,900 feet, where the pressure is several dozen times higher than at sea level. This kind of pressure would render gas bladders inefficient for maintaining buoyancy. Instead, the flesh of the blobfish is primarily a gelatinous mass with a density slightly less than water. This allows the fish to float above the sea floor without expending energy on swimming. Its relative lack of muscle is not a disadvantage as it usually just swallows any edible matter that happens to float by. Usually an invertebrate like a crab or sea pen. So, though they might not be the prettiest fish in the sea, the blobfish’s shape is highly functional. Although I wouldn’t recommend one as a pet…
Well, that was a fun topic. To see what the blobfish looks like on land, and a few witticisms, click here to watch my video.