THE AFTONIAN HORSES 349 



cies as the Gladwin horse. All the other inferior molars in the collec- 

 tions belong to the other type. The transverse diameters are less, the 

 cementum very meager, and the enamel is much thinner and more flex- 

 nous, as will be apparent on comparing figures 1 and 2, plate 19, with 

 figure 6 of the same plate. That these differences are not dependent on 

 age and wear is indicated by the fact that lower molars equally as short 

 as those of the Gladwin horse agree in essential features with 1 and 2, 

 plate 19. Figure 5 of this plate is an example of a short, well worn, 

 inferior molar of this type. The thinner teeth, with thinner and more 

 flexuous enamel, may be looked upon as teeth belonging to a species quite 

 distinct from the Gladwin horse and may be associated with the superior 

 molars which have been referred to Equus complicatus. 



Figures 3 and 4, plate 19, are external faces of the thin, almost cement- 

 less type of inferior molars, the grinding surfaces of which are shown in 

 figures 1 and 2. The tooth, figure 3, shows the effects of alveolar ab- 

 scesses from which the animal probably suffered seriously. Whether this 

 disease hastened the death of the individual may not be known, but it is 

 certain that life was cut short from some cause before the teeth were very 

 much worn. 



There are many equine bones from the Aftonian beds of Harrison and 

 Monona counties which, while more or less fragmentary, are in a fair 

 state of preservation. There are two humeri, right and left, each lacking 

 the proximal articulation. These indicate an animal about the size of 

 the average modern horse, the radius and ulna of the domestic species 

 fitting perfectly with the radial articulation of the fossil humerus. There 

 are portions of the radius among the fossil bones, four tibiae, four imper- 

 fect metapo dials, four first phalanges, and other portions of equine skele- 

 tons. The most perfect of the tibiae is comparatively small. The animal 

 to which it belonged was adult, but the size would indicate a rather small 

 pony. On the other hand, the distal ends of two of the fossil tibiae are 

 equally as large as the corresponding part of Equus cdballus, and the 

 same is true of the distal end of a fossil radius. The sides of the broad- 

 ened articular extremity of the Aftonian radius is abraded, making meas- 

 urements impossible, but 70 millimeters above the articulation both 

 modern and fossil bones are 60 millimeters in transverse diameter and 

 35 millimeters in thickness. The fossil metapodials are large and strong 

 and differ in cross-section from the same bone of the domestic species, 

 being more nearly circular in corresponding parts of the shaft. The 

 splint bones were evidently more rudimentary than in the modern horse. 

 Three of the first phalanges are as large as those of the present coach 

 horse; the largest one measures 92 millimeters in length, is 58 milli- 



