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 dog’s nose consists of a bony nasal cavity that is divided into two separate chambers by a bony and cartilaginous nasal septum. Within each of the cavities are the turbinate bones (conchae) and the paranasal sinuses.The turbinate bones form into several scrolls of moveable cartilage and bony tissue that is lined with ciliated epithelial cells.    The nose contacts with the environment through two holes, the “nares” and the ethmoid bone that marks the rear side of the nose. The inhaled air is warmed and moisted as it passes through the turbinates and the layer of mucus, which is a filter, trapping bacteria, particles and scents.    The dog collects scents by air, the volatile oils that travel in the air and by smelling the ground. The nares are fluctuate and allow during the diastole, more inhaled air, and during the systole, prevent the entry of undesirable objects.
When a dog smells, the scents are trapped in the mucus and processed by the sensory cells that are on the side. Several cilia extend into each of the sensory cells in the nasal cavity, and each of these cilia contains many receptors odor. After trapping the receptors from the cells smells, carting their messages through the ethmoid bone by neural routes directly to the olfactory lobe of the brain.
   From the olfactory lobe messages are transferred to the frontal lobes for recognition and other brain regions, including the brain centers for emotion, memory and pleasure. There are many connections between all these centers with a result of a simple odor detected by a dog, which probably has a whole series of concepts such as memory or emotional ties that only the dog can know and interpret.
I think it is easily noticeable that dog have much larger surface of nasal cavities and much more sensory cells to detect odors that human has. We know that the number of sensory cells can reach, depending on the breed, the 125 million, while human’s can reach only 5 million.
A huge area of the brain tissue, at the dog, deals with messages from olfactory cells. (Some estimates show that is about the one third of the brain).
So we are talking about an absolute specificity of the animal that is unavailable in other mammals, including human.

Jacobson Receptor
Inside the nasal cavity and opening into the upper part of the mouth there is the receptor Jacobson. The receptor Jacobson is a “sense of smell” that in fact is not receptive to ordinary odors.
Rather, the scenting nerve cells are quite different from those in normal olfactory tissue so to respond to various substances with large molecules, but often they do not detect any odor
The sensory receptor cells of Jacobson  (unlike any other nerve cells) do not communicate with the olfactory lobe of the cortex buIn fact, two separate but parallel systems that detect odors cooperate in a amazing way, so to produce sensitivities that we do not understand.
The primary function of the receptor is to detect pheromones, which determine the availability of the opposite sex for reproduction. Furthermore, the receptor is obviously able to identify other, usually undetectable, odors that can enhance, for example, the ability of the newborn to find his own mother.
Interestingly, although only a few years ago it was thought that the receptor Jacobson was not in humans, a recent anatomical study of 400 people confirmed the presence of it and the fact that neural connections are capable of sending messaging functions in the brain.
An additional argument in the theory of some religions that claim that human in not an animal.t with specific lobes and part of the brain that coordinates the mating and other basic emotions.