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Show 118 MR. H. G. F. SPURRELL ON THE [Feb. 6, have to act as grindstones. The comparative roundness of the condyle, the large extent of the articular surface over which it can play, and the presence of an emenentia articularis on to which it can glide, all contribute to increasing the range of these movements. The structures, moreover, are capable of considerable modification to meet the various requirements of ruminants, rodents, primates, <fcc. The mouth in Type 1 has to allow its possessor to seize and hold other animals, and for this reason the wide gape which the type allows is required. First the animal must bring its long canine teeth to bear on its prey; then it must be able to bring its hindmost molars directly to bear on the larger bones and the flesh of the prey. Therefore, in animals of this type, the corners of the mouth extend far back. Text-fig. 41. Diagram of jaws. Type 2. Showing lengthening of the jaws forward in order that the incisors m a y be widely separated whilst the molars are slightly separated and not thrown much out of the parallel. The mouth in Type 2 has to allow its possessor to crop grass or gnaw off pieces of roots, (fee. These morsels of food are then ground up by the molars. For neither of these purposes is a very wide gape required. A very slight separation of the molars is necessary; but in some animals, particularly the rodents, a rather wider separation of the incisors is required. As the progressive widening from back to front of the gap between the teeth is small when jaws of type 2 are opened, the jaws are often lengthened forwards. This allows the same movement which separates the molars at the back slightly to separate the incisors in front more widely (text-fig. 41). As it is only the incisors, not the molars, which are required to break up large pieces of food outside the mouth, the oral fissure is small. Another reason for this is that the molars require muscular cheeks to help the tongue in placing the food between them. It is perhaps the difficulty of striking a balance between the proper separation of the molars and incisors which keeps the angle E A C (text-fig. 41) greater than a right angle in animals with incisors. In animals like the Elephant and the Manatee, in which |