Now dogs, who doesn’t love dogs? With all due respect to dog-haters, they are one of the cutest species on animals on the planet earth, best pets, loyal, adorable. I could go on and on. No wonder they are called “man’s best friend”. Their scientific name is Canis familiaris and they are from the family called canids. They have been associated with humans for a long period of time and are finely tuned to human behavior. They perform many functions such as companionship, protection, herding, hunting, pulling loads, helping cops and military and also assisting handicapped humans.
Some interesting facts about dogs:
|Although dogs look very different from people, they share many of our body’s characteristics. They have a heart and circulatory system to transport blood, lungs to take in oxygen and rid the body of carbon dioxide, a digestive tract to absorb nutrients from food, and so on. However, it is the differences between dogs and people that are most interesting and that give dogs their unique characteristics as family members.
Dogs come in many shapes and sizes. The smallest breeds include the toy and miniature varieties, such as the Toy Poodle, Papillon, Chihuahua, and Shih Tzu. These dogs usually weigh only 5 to 10 pounds (2.3 to 4.5 kilograms), or even less. Medium-sized dogs include many of the terriers and spaniels, which weigh in the 10 to 50 pound (4.5 to 23 kilograms) range. Larger still are the retrievers, shepherds, and setters, which often weigh 65 to 100 pounds (30 to 45 kilograms). Finally, the giant breeds, such as the Mastiff, Komondor, and Saint Bernard, can approach or exceed 200 pounds (91 kilograms). Of course, sizes vary within breeds, with males usually being larger than females. Mixed-breed dogs include all size ranges.
Dogs have the same 5 senses that people do but to very different degrees. Some senses are less developed than in people, with others being extraordinarily more sensitive.
Dogs can see movement and light much better than people. In the retina of the eye, dogs have more of a specific type of cell called a rod, which is good at collecting dim light, so they have better night vision. A reflective layer in the dog’s eye, called the tapetum lucidum, magnifies incoming light. This reflective layer lends a characteristic blue or greenish glint to dogs’ eyes when light (for example, headlights of passing cars) shines into them at night. However, dogs do not have as much visual acuity as people, meaning that they cannot distinguish fine details as well. They also cannot differentiate colors as well because they have fewer of the cells in the retina called cones, which are responsible for color vision. Contrary to popular belief, however, dogs are not completely colorblind.
A unique feature of the dog eye is the nictitating membrane, which is also called the third eyelid. This additional eyelid is a whitish pink color, and it is found under the other eyelids in the inside corner (near the nose) of the eye. The third eyelid extends up when needed to protect the eyeball from scratches (for example, while traveling through brush) or in response to inflammation.
The ear canal of the dog is much deeper than that of people and creates a better funnel to carry sound to the ear drum. The average dog can hear about 4 times better than the average person, including sounds at higher frequencies than can be detected by the human ear. Dogs are also better at distinguishing the direction of a sound, which is an adaptation useful for hunting. Unfortunately, this deeper ear canal predisposes dogs to ear problems. Grease, wax, and moisture can build up in the ear, leading to inflammation and infection. Floppy ears or hair within the ears further limit ventilation, making matters worse. This is why many dogs need frequent preventive ear cleaning see Ear Disorders of Dogs: Ear Structure and Function in Dogs.
Smell and Taste
Dogs have an extraordinarily acute sense of smell; it is about a million times more sensitive than that of people. They can detect odors at extremely low levels and can distinguish odors that are subtly different. This is why dogs are able to sniff out drugs and explosives at airports, search for human victims at disaster sites (including victims deep under water), and follow the scent track of criminals.
Odor molecules dissolve in the moisture that coats the inside of the canine nose. Signals are then sent from the olfactory membranes in the nose to the olfactory center of the brain, which is 40 times bigger in dogs than in people.
Dogs also have an organ on the roof of the mouth that allows them to “taste” certain smells. As in people, taste and smell in dogs are closely linked. However, dogs gain much more information about food from smell than from taste. Dogs have only about one sixth the number of taste buds that people do, and their distinct sense of taste is actually quite poor.
Teeth and Mouth
Like their wolf ancestors, dogs are carnivores with teeth designed for rending and tearing meat. They have 28 deciduous (baby) teeth that are replaced by 42 permanent (adult) teeth between 2 and 7 months of age (see Description and Physical Characteristics of Dogs: Canine Adult Dentition). The different types of teeth have specialized functions, depending on their position in the mouth. The front teeth, which include the 12 incisors and 4 large canine teeth (eye teeth), are designed for grasping and tearing. The rearward premolar and molar teeth grind food into smaller pieces that can be swallowed.
The mouth also contains the salivary glands, which secrete saliva that lubricates the food and begins digestion. The tongue helps guide food to the back of the throat and is important for licking up small food pieces and lapping up water. Dogs also lick as a sign of affection or subservience, or both.