Here we consider the body structure and special senses of the cat and dog. For body structure we'll look at skull and dentition, paws and claws, and the hair coat, and we'll consider the special senses of vision, hearing, and olfaction.
Let's begin with the body structure of the cat. As we move through the lecture always be thinking of how these animals originally lived as predators. Their body structure was built for speed and for the detection, pursuit, and capture of prey. This is reflected in the distinctive modifications of the cat's skeleton, which provides much flexibility to the animal.
Cats have a vestigial clavicle, which allows enhanced mobility of the front legs, and that aids in chasing and catching prey.
The joints between the vertebrae are also extremely flexible, and that helps with flexion and extension used in climbing, stalking, and pouncing.
The hind limbs are also specialized in cats in that the musculature provided tremendous power for jumping and leaping, as opposed to animals who can travel long distances.
Now this flexibility contributes to one of the trademarks of the cat—his superb balance and coordination. The tail certainly serves an important function in establishing and maintaining balance, as well as something called the vestibular apparatus. This is the main organ of balance in a cat's body, and it's a specialized structure located in the inner ear, which provides information to the brain regarding movement, changes in direction, acceleration, gravity, and linear motion.
Now we'll consider the cat's skull. The cat has a short face compared with other domestic animals. The jaw is short, providing power, and can open very wide. The associated musculature facilitates grabbing and holding prey.
Now different breeds have more or less round or angular faces, with the most dramatic alterations being in the length of the head or muzzle. For example, at the top here you see a Persian, which has an extremely short muzzle as part of the breed's standard. At the bottom is a domestic shorthair, showing a more common and moderate muzzle length.
Now when we consider dogs, we know that the body structure too developed originally for speed and predation, but original working roles and later selective breeding led to extreme differences in body size and body proportion among the breeds. Some of the biggest differences among breeds are observed in the skull.
There are three basic skull types of the dog based on skull based width and muzzle length. Building on the root cephalic, which means head, we have dolichocephalic (meaning long head), mesaticephalic (which is a middle or medium head), and brachycephalic (meaning short head).
The dolichocephalic head type is represented by narrow skull base and elongated muzzle. The functional purpose of this head type is speed, and it's usually accompanied by a long neck. This is the head type that's typically represented in sighthounds, such as greyhounds or Salukis.
The mesaticephalic head type is the moderate head shape, with medium skull base width and muzzle length. Now, shortening the muzzle length tends to create a stronger jaw, so we see this head type in breeds developed to carry, such as retrievers.
The brachycephalic head type has an extremely broad skull base and short muzzle. The short compact muzzle confers great jaw strength. This is typical for breeds that were originally developed for fighting, as well as some toy breeds because it's an example of neoteny or pedomorphosis since this round, large head proportional to body size is a puppyish characteristic.
Now let's consider dentition. Cats and dogs each have their own modification of a general carnivore dental pattern.
We'll begin with the dentition of the cat and look at the different types of teeth present.
This view shows one half of the skull.
Each upper and lower jaw has three pairs of incisors. The function of the incisors is grooming and tearing prey.
Each jaw also has one pair of elongated canines, which interlock when the jaw is closed. The function of the canines is for grasping and killing prey.
Cats have three pairs of premolars on the upper jaw and two pairs of premolars on the lower jaw. The premolars aid in chewing and grinding food.
The cat has one pair of molars on each the upper and lower jaw. Molars also are used for grinding food.
There is also a special designation of four teeth known as the carnassial teeth. The carnassial teeth are made up of the last upper premolar on the top paired with the lower molar. These teeth are laterally flattened and provide shearing action for cutting food into small pieces before being swallowed. Carnassial teeth are a signature of carnivore dentition.
So if we add up these different types of teeth, the adult cat has a total of 30 permanent teeth.
Let's compare that to dogs now.
Adult dogs have more total teeth than cats at 42. Again, the dog dentition fits a general carnivore pattern. Each jaw has three pairs of incisors and one pair of elongated canines which interlock. Compared to the cat, the dog has more premolars and more molars. Each jaw contains four pairs of premolars, and there are two pairs of molars on the top and three pairs on the bottom. Since premolars and molars function to crush and grind, their greater number here reflects the fact that the dog has a more omnivorous diet than the cat and needs to crush and grind fibrous food in addition to tearing meat. Note also that the dog has a pair of carnassial teeth formed by the last premolar on top and the first molar on the bottom jaw.
So far we've considered the adult dentition pattern, but now let's take a look at deciduous dentition. Dogs and cats have two sets of teeth during their lifetimes. The differences between puppy teeth and an adult dog's dentition, or between kitten teeth and an adult cat's teeth, is that the puppy and kitten do not have molars. The need to crush and grind food is not present in the young animal's earliest weeks.
So for dogs there are 28 deciduous, or puppy, teeth and 42 adult teeth. Kittens have 26 deciduous teeth and 30 adult teeth. Now when does this transition occur?
This timeline illustrates when the deciduous and permanent teeth erupt in cats and dogs. The deciduous teeth typically erupt around 21 days of age and are fully erupted by five or six weeks. The permanent teeth, then, erupt to replace the deciduous teeth around four months and are completely erupted by six months.