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Show 1906.] ARTICULATION OF THE VERTEBRATE JAW. 119 the lips do the work allotted to the incisors of most other herbivora, the angle is far nearer a right angle. The skull of the Dugong (in which horny plates take the place of incisors) seems to attempt another solution of the difficulty. Another angle is introduced into the jaw, bringing the anterior third of the jaws into a line parallel with the ascending ramus (text-fig. 42). A less marked tendency to introduce the second angle may be seen in some other animals:-among the Pigs, in Sus longirostris; among the Ruminants, in the Chevrotain Tragulus javanicus (text-tig. 43). Text-fig. 42. Diagram of jaws. Type 2. Showing the introduction of a second angle to procure wide separation of the incisors with slight separation of the molars. Text-fig. 43. Skull of Tragulus javanicus. Having briefly studied the principle in the Mammals, I next turned to the Reptiles. Most of these have jaws of type 1 : the lower jaw articulates with the skull in the plane of the teeth. The Snake, however, has a mouth in which (owing to the great mobility of the quadrate) the jaw-principles of type 1 and type 2 are combined in a very remarkable manner. |