Comparisons between the movement of the jaw of a carnivore and that of a herbivore

Herbivores and omnivores have evolved specialised muscles and dentition in order to sufficiently masticate their vegetation to allow for adequate digestion of the feed intake. Herbivores, when compared against carnivores, have a pronounced masseter muscle, which initiates and aids the movement of the jaw in a lateral movement, which grinds food on the flat molar dentition at the back of the mouth. An animal that can live solely on a vegetarian diet should have a pronounced masseter muscle to help break down the strong cellulose walls that would otherwise prevent the absorption of proteins and fat within the plant cell. Carnivores, however, have a masseter muscle that is smaller in size, due to the fact that the muscle cannot move the mandible in a lateral movement due to the shape of the jaw. It is noted in Dyce (1987), that the only movement of the mandible in a lateral movement will cause trauma, and is 'occasionally so severe that the coronoid process engages the zygomatic arch, locking the jaws in the depressed position'. This problem occurs due to that the mouth of evolved carnivores, such as the dog and cat having the scissor-like movement of the jaw bones, and the postglenoid process prevents the temporalis muscle from dislocating the jaw. This would evidently be possible because the temporalis muscle is a powerful muscle that joins the mandible to the top of the cranium by stretching from the large coronoid process in carnivores to the occipital region. The pronounced zygomatic arch on a carnivore's skull shows that it is bowed to allow the large muscle to work properly. It is believed that the temporalis muscle evolved to restrain prey species for consuming (Dyce, 1987; Pough, 2002). A strong temporalis muscle wouldn't have evolved as much as the cat, which is defined as an obligate carnivore.

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