. Elementary text-book of zoology. Zoology. THE ALIMENTARY CANAL. 287 ire changed constitute the milk ili'ittitimi. The anterior which with the incisors and canines are replaced, are known as the prcemolars, as opposed to the posterior, true molars, which belong to the permanent dentition, and are not replaced. The true molars only appear after the milk teeth have been replaced, and are distinguished by the size and number of their roots, as well as by the extent of their crowns. Formula?, in which the numbers of incisors, canines, prsemolars, and molars in the upper and lower jaws are i^iven,
. Elementary text-book of zoology. Zoology. THE ALIMENTARY CANAL. 287 ire changed constitute the milk ili'ittitimi. The anterior which with the incisors and canines are replaced, are known as the prcemolars, as opposed to the posterior, true molars, which belong to the permanent dentition, and are not replaced. The true molars only appear after the milk teeth have been replaced, and are distinguished by the size and number of their roots, as well as by the extent of their crowns. Formula?, in which the numbers of incisors, canines, prsemolars, and molars in the upper and lower jaws are i^iven, are used to indicate in a simple manner the nature of the dentition, , the dental formula of man is 2123 r • -2-2 1-1 ::•:;• 2123 t. 2-2 IJ. 2-2 -"- 1*1 - - tructures at the C r>. Alimentary canal. In addition to the hard entrance to the digestive cavity, soft, movable lips which bound the mouth opening, and a fleshy tongue which is of very various form and lkjs on the floor of the buccal cavity, are of special importance for the introduction and preparation of the food (fig. 675). In the Monotremata the lips are replaced by the edges of the beak. The tongue, however, is never absent, but it may be im- movable, and completely fused with the floor of the mouth, as in the Whales. Its front part is mainly tactile in function, but in some CMM - it is used to seize (Giraffe) or capture food (Ant-eaters). Variously shaped papilla?, which are often cornified and bear recurved hooks, project from its upper surface. The papillce circuit) rnffafir alone have a relation to the sense of taste. The tongue is supported by the hyoid bone and by a cartilaginous rod, which represents the OK interglossum (Lyttc/b). The anterior cornua of the hyoid are attached to the styloid processes of the temporal bone, the posterior bear the larynx. Beneath the tongue there is sometimes (most developed in the Insectivora) a single or double projection, which is termed the lower tongue. The
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
