314 



DR. H. GADOW ON THE SPECIES OF RHEA. [Mar. 17, 



Makes 33 vertebrae between the occiput and the primitive inter- 

 sacral nerve, which in all the three species is the 34th spinal nerve, 

 no matter whether being at the same time the last ischiadic root, 

 without connection with the pubic plexus as in Rh. macrorhyncha, 

 or beingin connection with the ischiadic plexus by a ramus communi- 

 cating only and belonging chiefly to the pubic region, as in Rh. 

 darwini $ . 



We have therefore to compare the series of the first 15 vertebrae 

 of Rh. macrorhyncha with the first 14 vertebrae of the other two 

 species. There can be no doubt now, that the greater number of 

 neck-vertebrse is not produced simply by a shortening of the first 

 pseudo-thoracic rib, as it generally happens in apparently similar 

 cases of variation in the number of ribs, but, on the contrary, that 

 the whole of the thoracico-lumbar region has been affected by a tail- 

 ward " shifting " to the extent of one metamere ; and it is also abso- 

 lutely certain that the serial differences between Rh. americana and 

 Rh. macrorhyncha have not been brought about by the inter- or 

 ex-calation of a vertebra. 



In order to determine whether Rh. macrorhyncha possesses a pro- 

 portionately longer neck than the other species, we have to compare 

 the length of the neck to some distance which must stand in some 

 reasonably conceivable correlation to the former. 'i'he distance 

 between the neck and the acetabular region appears to be rather 

 advisable for this purpose. Again, one may fairly well suppose that 

 in essentially terrestrial birds there might be a correlation between 

 the length of the neck and the length of the hind limbs. However, 

 the elevation of the trunk above the ground depends not only upon 

 the length of the hind limbs, but also upon the angles formed by 

 various segments of the hmb to each other and to the pelvis. These 

 considerations therefore leave the following results open to doubt. 

 At any rate I have made the calculations, in which a certain limit 

 of error in measuring the neck and hmb must be allowed. 



E. darwini $ , 

 centim. 

 Length of neck from atlas to 

 cephalic end of transitional 

 (14th or 15th) vertebra.. 527 

 Length of fenmr + tibia -\- 



tarso-metatarsus 88-3 



R. americana. 

 centim. 



57-0 



87-4 



S. macro- 

 rhyncha. 

 centim. 



47-5 

 73-1 



If the neck of Rh. darwini were of the same proportionate size as 

 that oi Rh. macrorhyncha, there ought to be 



52-7 : 88-3=47-5: 73-1 

 but 52-7X 73-1 =3852-37 

 8S-3x47-5 = 4194-25 



