474 BARON FRANCIS NOPCSA ON THE 



A hypothesis that assumes that organs that develop in one 

 part should be capable of spreading on to adjacent regions where 

 they are of little or no value, needs naturally to be proved. 



In all species of Rhinoceroses in which a strong nasal rugosity 

 is present to serve as base for the dermal horns, the surface of the 

 jugal a.ich, the lacrynial, prefrontal, the otic region, and even 

 the posterior and exterior surface of the mandible, is also lOugh 

 {Rh. suinatrensis, Rh. hicornis). In those Rhinoceroses, however, 

 in which the nasal tuberosity is weak or wanting, the jugal and 

 lacrymal and the other bones mentioned above are also smooth 

 {Rh. unicornis, Aceratheo'ium). 



A similar feature, as in Rhinoceros, can be found also in 

 Suidse, Hylceoclioirus does not only show strong rugosities on 

 the maxillaries and jugals, where the facial warts are developed, 

 but also on tlie mandible and the frontal. S^is verrucosus 

 shows similar but less marked features. Contrary to this, in 

 ^S''/is harhatus and Sus cristatus all the skull bones are smooth, 

 and correspondingly on the cheeks strong warts and rugosities 

 are wanting. 



That the rapidly spreading rugosities in Rhinoceros and Sus, 

 though in connection with waits, do not exclusively depend on 

 the presence of these excrescences, can be demonstrated by the 

 difi'erent Girafi'es. Also in the latter a spreading of exostosis is 

 traceable until the whole head is covered and even the mandible 

 is afiected : nevertheless, the skin in these animals remains smooth, 

 and is quite noi'mally covered with hair. Less clearly than in 

 thesft three groups, the spreading of useless exostosis can be 

 observed in the bovine ti-ibe. In Bos hubalis, Bos gaurus, and 

 the Bison, all of which have strong bony horn- cores, the 

 rugosities of the frontal spread to the orbital and otic region, 

 while in Bos depressicornis, in which the horn-cores are weak, 

 the orbital and otic region is smooth. Bearing all these facts 

 in mind, and they could easily be multiplied, and considering 

 furthermore that in Crocodiles the skull bones and the bones of 

 the dermal armour are of altogether different origin but that 

 they nevertheless show the same pattern of sculpture, and that 

 thus also they sliow the spreading of one feature over the 

 whole body and that something similar occurs in Lepidosteiis (8), 

 I think it is not too much to assume that also in the j^rimitive 

 Proavis the primitive feathers of the tail spread even to regions 

 where they were not wanted. Their attachment on a patagium 

 is the best proof that they never functioned. That the primitive 

 feathers of birds were quills and not, as generally thought, down 

 was recently proved by Steiner (17). 



In this way also Beebe's chief argument for the reconstruction 

 of his Teirapteryx loses a great deal of its value. It only shows 

 that first in birds only a marginal row of quills was developed 

 on the arms and on the tail, that later these spread towards the 

 feet, and that the rest of the quills spring up later. 



Summing np, one can safely state that in the skeleton of recent 



