1. The Origin of the Dog

 

2.The dog's evolution

 

3.The Origin of the Dog Revisited
1. The Odyssey of the Word "Molossus"

2. The Evolution of brachycephalic molossoid dogs

1. Man's relationship with animals

2. Dog and Human societe

3. The dog shows in Europe

1.The Vision in dogs

2. The hearing of the dog

3. The sense of smell in dog

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THE SENSE OF HEARING IN DOGS.
To understand how dogs hear, we need to understand the anatomy of their ear. The ear in dogs is similar to that in all mammals, differentiated according to the evolutionary adaptation of the dog.
Structure of the ear
 Puppies are born deaf. Until the age of 10 days the ears are sealed and they need around 15 days to begin perceiving some sounds. By the end of the first month, the development of the inner ear is completed and so the sense of hearing starts operating normally
The ear is consisted of four parts, the flap (external speaker), the external auditory canal, the middle ear and the inner ear. Depending on the breed there may be also a different flap that has the ability to move independently of one another.
The flap is filled with many muscles for the control of movements, many blood vessels that contribute to regulation of body temperature (along with panting and sweating of the feet), and nerves. It is mostly cartilage, covered with skin. It bears hair and the inner part, depending on the breed, can be nude or partially hairy. More than 18 muscles help control movement at the base of the ear, allowing optimal capture and audio input (like a satellite dish).
The outer ear or ear canal is a tube from cartilage, coated with both responsive and sebaceous glands, producing a protective coating like wax, the cerumen. This tube from cartilage is what we call external auditory canal.
The middle ear consists of three small bones called the hammer, anvil and stirrup. A tube, called the Eustachian tube, connects the mouth with the middle ear and allows air to enter into the middle ear, helping to balance pressure in the drum (we understand this when we ascent to high altitude in a short period of time) (Video representation)
The inner ear contains the cochlea, vestibule and semicircular canals. The cochlea is filled with fluid and specialized cells like hair, used to detect acoustic vibrations which are transferred directly through the auditory nerve to the brain. The tiny hair cells vibrate depending on the exact frequency audio receiving. The semicircular canals are parts filled with liquid and they are used to maintain the balance of the organism with the environment. Any shift in the position of the head displaces this fluid and so this change of position is detected by the brain. This tells the dog about the position of its body. (That is it works like the bricklayer’s spirit level, that no matter how you place it, the bubble of air is always on top and horizontal.).
What do the dogs hear.
It is considered that dogs perceive sounds better than the man, but this just is not so. The truth is that they understand the sounds a little better, "... maybe a few hundred times better and some frequencies they can understand in a better way…”, says Coren.
Essentially a dog can detect better very high frequencies, such as the rustling of leaves or the noise of rodents when marching on leaves and hissing cries of small prey. And it seems that this sensitivity is a result of dog’s adaptation to hunting these small animals for feeding and survival. This ability varies between 3.000 herz and 12.000 herz in the dog. (Coren, 2004).
Perception of direction and distance.
Dogs have a unique way to identify the direction of the sound. They need this ability to find prey, receive signals of impending danger and at the same time determine about the direction of escape. The ability of dogs to identify the direction of the sound is due to the different position of the ears. This is understandable because the sound that reaches the proximal ear will be slightly louder and then, a fraction of a second later, reaches the farthest ear. The time delay between the two ears is increased for dogs with larger heads. The increased distance between the two ears gives an increased advantage for determining the distance from where the sound comes.
As in humans, the ability of dogs to hear decreases with time. Other reasons for hearing loss are ear infections, trauma, loud noises, heredity, clogging caused by excessive cell, foreign items and infections of certain drugs. Congenital deafness occurs in certain breeds such as the Australian Shepherd, the Great Dane and Dalmatian and has been linked with the gene "merle", which is responsible for repainting those who call blu merle and speckled colors present in the body. (Lindsay, 2000).
The position and shape of the ear varies with the breed. So we find upright ears, either pointed or rounded at the tip, narrow or wide, half-upright and fallen. For droopy ears there are many opinions related to the reason the ears of a predator are droopy. We know that no wild animal has drooping ears, while many dogs have ears so drooping that they are no longer able to move comfortably due to muscular debility and weight, because of their size.
A lot of people think that this is the result of cross-fertilization done by human, especially for tracking breeds and is considered that large loose and droopy ears act as odor trapping funnel around the nozzle, thus facilitating their capture. For others the droopy ears are not the result of human act, but a natural selection and are also found in dogs long before man started cross-fertilization in dogs (Egyptian mummies) and consider that simply hearing has been reduced thanks to the other dog's abilities as smell, sight, taste.
However the upright and pointed ears characterize predators which capture low-frequency sounds and catch generally smaller than them prey, while dogs with upright ears and rounded edges, are mostly predators which catch larger prey than those. So, in order for a sound to be perceived, regarding to its frequency, the corresponding shape of the instrument is needed for the best result.
Flap position (hearing), the position of the eyes (vision) and the type of teeth (nutrition) are the sizes that define the shape and size of the skull.
Besides all these, the ear of the dog is also a good indicator of feelings. Eg when the dog holds the ear flaps continuously folded backwards and when the tips of the ears point forwards and down, we are talking for an upset dog. When the edges point downwards and sideways, than we have disruption and curiosity of the animal.