. Guide leaflet. molars comesto fit between them. The protocone of Osborn is apparentlv^ not the oldest cusp of theupper molars but arises as a swelling or bud on the inner side of the baseof the crown. In the earlier stages the outer part of the crown, called the cingulum,is very large, but after the fourth stage (from the bottom) it disappears,leaving the paracone and metacone on the outer border of the crown. In the fifth stage a new cusp, the hypocone, grows up, filling the spacebetween the upper molars and changing a triangular into a roundly quad-rangular crown. In the lower molars we ob
. Guide leaflet. molars comesto fit between them. The protocone of Osborn is apparentlv^ not the oldest cusp of theupper molars but arises as a swelling or bud on the inner side of the baseof the crown. In the earlier stages the outer part of the crown, called the cingulum,is very large, but after the fourth stage (from the bottom) it disappears,leaving the paracone and metacone on the outer border of the crown. In the fifth stage a new cusp, the hypocone, grows up, filling the spacebetween the upper molars and changing a triangular into a roundly quad-rangular crown. In the lower molars we observe that in the earlier stages the talonidsor heels are small, but finally they become larger than the trigonids (orlower triangles). As this happens, the protocones of the upper teeth enlargeto fit into the expanded talonid basins. The paraconids, or antero-internalcusps of the lower molars, disappear at the fifth stage, while the hypoconesof the upper molars become enlarged. C5O INTRODUCnON TO HUMAN ANA lOMY. @ ® 0(^^<^ Fig. 28. EVOLUTION OF MOLAR TEETH ILLUSTRATED BY FOSSIL AND RECENT MAMMALS. Upper teeth left, lower teeth right half of picture. A. Pantotherian. B. Deltatheridhmt. C. Fotamogale. D. Didelphodiis. E. Fronyctice- bus. F. Dryopitheciis. G. Le Moustier. H. Man (modem White) 1:533 THE NFR\ OLS SYSTEM AND ITS FUNCTIONS ELEMENTS OF IHE NERVOUS SYSTEM(CASK \ IIB) Alan, like other organisms, is a living solar engine, run bv the energ\ ofthe sunlight that is stored in plant and animal food (see Case I). This stolen energy mav easily drive its user to destruction unless quickadjustments are constantly being made against dangerous forces both insideand outside the body. The nervous system makes these adjustments possible; it also determineswhich one of several alternatives shall be followed when competing interestsare at stake. In very simple animals a good adjustment is presumably re-warded by a sense of \\ ell-being or pleasure, \\ hile a bad adjustment givesrise
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