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Home , Eohippus, Neohipparion

Neohipparion, A Three-Toed By CHESTER STOCK

0 other lineage of -' illustrates quite so are elevated above the ground and no longer function clearly or so full$ its growth or evolution in geo- a supporting elements of the foot. In the retention of Nlogic time as that of the horse. In the history of the the lateral digits the were distinctly less pro- many forms antecedent to the living are gressive than the contemporary and monodactyl Pliohip- now known, each marked by readily identifiable charac- pus, and it is from the latter that Equu~is now regarded ters in the teeth, skull and skeleton. From , to have sprung. the "dawn horse" of approximately 50 million years The group persisted through the , ago, to the equines of today, a score or more different hut disappeared with the coming of the Pleistocene or kind3 of genera and numerous species of extinct horse* Ice Age, at least in North America. During the late have been described. The changes that have produced or early Pliocene. the true hipparions are found the large and specialized animal of today from the in North America and Eurasia. By the middle of this diminutive and distinctly less specialized ancestor epoch. perhaps eight or nine millions of years ago. these of long ago are demonstrated by an amazing array of gave ua; to the larger. heavier neohipparions fossil remains. fonnd for the most part in the land-laid which were characteristically North American in distri- formations of the western United States. bution. They have been found fossil. for example, in Tracing the evolution of the Equidae involves not on]\ Florida. Texas. the western Great Plains. the Great Basin a determination of those kinds of horses that were in province, California and Mexico. Although described the lineal descent to modem , hut, likewise, a rec- from a number of localities. nowhere has a specimen ognition of the types that belonged to collateral branches been fonnd sufficiently complete to permit the construc- of the family tree. Among the latter are the hipparions tion of a mounted skeleton. and their offspring of the Pliocene. These horses, on the During one of the early expeditions of the Division of basis of the progressive characters of their teeth, were the Geological Sciences, California Institute, well-pre- once regarded as ancestral to the existing Equu. They served materials of the species leptode are, however, creatures that have persistently retained were uncovered in the middle Pliocene, Thousand Creek three toes in front and hind feet. although the side toe* deposits of northwestern Nevada. These have now been prepared by E. I,. journe\. mill this rcrult in improving and increa-iing Furlong, and an our mental ability. with beneficial progress? exceptionally fine PROSPERITYÑDEPRESSIO skeleton fF;gs. 1 and 2) the first of We have seen that many of the notable civilizations its kind. has been of earl! history. the Egyptian. the Carthaginian. the mounted by Wil- Chinese. the Incan. and the Roman. during tl~rheight liam Otto. prepar- uf their power. built hard surfaced roads over which ator in Vertebrate the civilizing influence- from anv portion of the empire pale onto lo^. could How to any other portion. AH of these early civ- The skull in thie ilizatioiis reached a peak, and declined. their road sys- animal is of an terns deteriorating with them. It is impossible to deter- adult male. The mine which was the cause and which the effect. hut it is skeleton as it interesting to note that a decline of one element accum- stands compares ~anieda decline of the other. in size with that of In the early 1930's the linitrtl States experienced tin- the Burchell zebia. worst depression in its history. The depression was more being a trifle over than nation-wide: it was world-wide, and many able stit. 3 feet 9 inches, or dci~lsmarked it as the begin~~ingnfthe end of our mod- approximately ?rn civilization. Road huildingclecreased materially in 113% hands, tall at the linited States in this perioO. There was very little the withers. How- new construction, and many existing roads were allowed ever. the propor o deteriorate through lack of maintenance. Later. a tions of thie Plio- ilefinite increase in road Imilding occurred. which in cene horse are no- turn. was greatly slowed in war activity. In spite of this ticeably different check. some major projects. such as the Alaska and Pan- from those of mod- American Highway.. have been materially rushed for- ern Equus. A strik- ward. adwe have a very practical hope in the ?cars to ing difference i- come of "eater and more extended international hi")- seen immediate!\ va! travel than ever. it has ofirn been contended that in the small size theae international highway ma! constitute one of the of the head. In the 'reatest civilizing influences of modem times and it fossil specimen the seems not too much to expect that we may still progress skull i* tlistinctl) it11 roads. smaller in relation to the size of the body than it i~ in Buried Voice Channels the zebra. While ICimli~ii~c~!from PwII) the body is pro- amount of protection desired against possible damage to portionately as FIG. 2 the cahle. Even at these depths some little trouble is Ionps in the Bur- caused by lightning in those areas where electrical storms chell zebra, the sides are flatter, the clie-t appearing arc common. A number of installations have been made narrower and "slab-sided." The limits arc. likewise. dif- I II~Ione or more copper lightningprotection or ferently proportioned. the principal hone9 of the fore shield conthictors have heen buried above the cable. hut and hind feet being very much longer in relation to the these have not been completelv effective. Some considera- arm and thigh hones. respectivel!. than they are in the tion is now beinoiven to the use of a copper sleeve zebra. This extra length in the feet of Vco/tippunon covering the normal lead sheath of the cable itself. caused its limbs to he some six per cent longer. in rela- To determine the existence of current on the cable tion to the size of it* bod! than even the highly-special- heath. a recent installation was equipped with test points ized limbs of the modern race horse. The tide toes are approximately every 3.fHH) feel. At these locations. two beautifully preserved. and. as shown in the 4eleton. are es permanently attache11 to the cable sheath. 10 feet art and insulated from the earth. were brought to the face am1 terminated in a housing for the convenien the tester who makes periodic checks of the curre fissure. In running. ,Veohippfirion ngnnthe cable sheath. Periodic tests are necessa the speed of the zebra. at least f . despite the fact that the cable is buried, there are The mammalian associates o imlw of causes for changes in the effectiveness of t when it roamed the grasslands nlation, not the least of which are the rodents, o Thousand Creek region of no fleet gophers previously mentioned. Only that part of c United States roughly east of the Mississippi Riv exchtsive of an area in the Southeast, is free from th -1s. AS PROTECTS CABLE FROM MOISTURE rice the paper insulation of the e ilv absorbs water. ever) effort must from P (Continued moisture. Even a small amount of ie insulation resistance and a little hit more ma) short- rc~iittho or more conductors and pot circuit;, out ¥nice To protect the most important cables from t entrance of moisture and to provide a means of detpftin-

ENGINEERING AND SCIENCE MONTHLY