Farr.] 154 [May 15, 



so-called hypostyle, is less well developed in the deciduous molars than 

 in those of the permanent set. 



2. D. 2 is much larger, more elongate antero-posteriorly, more com- 

 plex, the antero-external buttress being much larger and more distinct 

 in the earlier set. It is so large that it might almost be considered a fifth 

 principal lobe. 



3. The median accessory lobes (5 and 6) are more conical than in the 

 permanent set, where they are somewhat appressed. These lobes in the 

 early set are separated by a distinct notch from the internal lobes. 



4. The transverse ridges are more nearly confluent with the outer wall 

 of tooth in most of specimens in the temporary set. There is, however, 

 great individual variation in regard to this character. 



5. In the adult skull all the molars and molariform premolars are 

 much wider transversely than antero-posteriorly. The deciduous teeth 

 are more nearly square, the two diameters being subequal. 



6. The buttress on the antero-exteriial lobe of tooth, the parastyle, is 

 better developed in the milk set. 



7. D. 2 is the longest tooth of the milk series and is beginning to 

 assume the elongate character of this tooth in the modern horse, while 

 the corresponding tooth of the permanent set is smaller than any of 

 the other molar teeth. 



8. All the temporary teeth are shorter in vertical height than those of 

 the permanent set. 



The Vertebral Column. 



The cervical and dorsal vertebrae have already been minutely de- 

 scribed. The lumbar vertebrae are almost certainly five in number. 

 The centra are large and are reniform in shape, being wide transversely 

 and not having the more nearly circular outline of the median dorsal 

 vertebrae. All of the lumbars, with the exception of the last, have their 

 centra strongly keeled. The centra are moderately opisthoccelous. The 

 interlocking character of the vertebra; through the zygapophyses is 

 marked. The neural spines are long, transversely compressed and 

 narrow and have considerable antero-posterior extent. They are all 

 directed forward at an angle. The transverse processes are well devel- 

 oped and widely expanded. The intervertebral foramina perforate the 

 bases of the neural arches, and are not merely notches in the ends of 

 the neural arch as they are in the anterior vertebrae of the column. The 

 last two lumbar vertebrae have their transverse processes expanded 

 almost as widely as those of the first sacral itself, and the transverse 

 processes of the fourth lumbar abut against those of the fifth, while the 

 latter bears on the posterior surface of the transverse processes deep 

 concavities for the corresponding surfaces of the anterior end of sacrum. 

 An analogous condition is seen in Equus, and in old individuals the last 

 two lumbars are very frequently immovably coiissified. The last lumbar 

 lias the spine more nearly erect than that of the penultimate luml)ar 

 vertebra. 



