OCR Text |
Show 1885.] DR. H. GADOW ON THE SPECIES OF RHEA. 315 Since we want to know the proportion of the neck, we must leave the limbs unaltered, but shall have to increase the index for the neck of Rh. darwini in order to render the proportions of the equation correct. This would be the case if the neck of Rh. darwini were about 57'3 centim. long instead of 52'7. Consequently the neck of Rh. macrorhyncha is proportionately longer than that of Rh. darwini. Again, the corresponding figures for Rh. americana and Rh. macrorhyncha are 4151 and 4191, sufficiently agreeing (considering errors of measurement) to show that the proportionate length of the necks of these two species is the same. Rh. americana compensates the shortness of its neck, caused by the smaller number of neck-vertebrae, by the shortness of its hind limbs. As we come to the conclusion that Rh. americana has the shortest hind limbs (p. 316) we can look upon these calculations as checking each other's correctness. Whether compensation be effected also by a greater length of the single cervical vertebrae, it would be very difficult to find out. Lastly the corresponding figures for Rh. americana and Rh. darwini are 5033 and 4606, again showing that we should have to increase the index for the neck of Rh. darwini to about 57*5 in order to get a correct equation. This proves beyond doubt that Rh. darwini has the proportionately shortest neck of the three species, and the more so because it possesses the largest hind limbs. The length of the neck, expressed inper cent, of the whole vertebral column from the axis to the acetabular vertebra, is Rh. darwini 59, Rh. macrorhyncha 61'68, and Rh. americana 6195. It was interesting to find out whether there existed a correlation between the limbs and the neck and trunk. The following measurements show, first, that Rh. americana and Rh. macrorhyncha agree almost absolutely with each other in the proportions of their limbs to the acetabular-atlas distance ; secondly, that there exists a correlation between the distances applied, unless we attribute to mere coincidence the fact that the same results are arrived at by different calculations. R. darwini. R. macrorhyncha. R. americana. centim. centim. centim. Length of femur + tibia + metatarsus 88*3 73-1 87*4 Length from atlas to acetabulum 88-7 77*0 92*0 73*1x92=6725-2 87*4x77 = 6/29*8 |