No. 2.] THE RELATIONS OF PROTOCERAS. ^^^ 



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The thoracic region is of about the same length as in 

 Moschus and of similar general appearance, but a comparison 

 of the two genera brings to light a number of differences in 

 the details of structure. Thus, in Protoceras the transverse 

 processes are decidedly longer, especially in the hinder part of 

 the region. In MoscJms the spines of the posterior vertebrae 

 are lower, but much more extended from before backward, 

 especially at the tips, which from the tenth to the thirteenth 

 are thickened and project beyond the spine both in front and 

 behind. In this genus also the ninth, tenth and eleventh 

 vertebrae have metapophyses, which are particularly prominent 

 on the tenth and eleventh. In the fossil these arise near the 

 ends of the transverse processes. 



The Lumbar VertcbrcB (PI. XXI, Fig. 9) numbered at least 

 five. In the anterior region the centra are shaped like those 

 of the posterior thoracic series, but as we pass backward, they 

 become more and more broadened and depressed ; the centrum 

 is longest in the second, third and fourth, slightly shorter in 

 the first and considerably so in the fifth. The zygapophyses 

 are of the usual cylindrical, interlocking, artiodactyl type, but 

 no episphenial processes are developed. Large and conspicuous 

 metapophyses are present, which in MoscJuls are hardly more 

 than rudiments. The neural arches and spines are more 

 traguline in shape and appearance than pecoran ; the arches 

 are short from before backward, being deeply cleft between 

 the postzygapophyses, which is not the case in MoscJuis, and 

 the pedicels of the arches are not perforated by the spinal 

 nerves (as they are in the modern genus) which pass out 

 through the notches below the postzygapophyses. The spines 

 are less extended antero-posteriorly than in the musk-deer and 

 resemble rather those of Tragidus, being slender and curved 

 forward. The transverse processes are likewise quite different 

 from those of MoscJnis. In the latter they are slender and 

 depressed, extending downward as well as outward, and are not 

 at all like the broad, plate-like processes of the higher Pecora. 

 In Pi'otoceras, on the other hand, they are long, very broad and 

 thin, rounded at the tip and but slightly decurved, and are thus 

 of the typical pecoran shape. The process is quite short on 



