678 



Dritte Sitzung der sechsten Sektion. 



borne by a single individual are rarely if ever precisely symme- 

 trica! in size, weight, form, or even in the number of points. 



The reduction of the number of caudal spines was also due 

 to the evidence offered by two other specimens, again in the 

 U. S. National Museum, with the spines in situ. One of the 

 cotypes of Stegosaurus ungulatus, however, shows four pairs and 

 no further evidence of the duplication of bone so that it is evident 

 that they all belonged to one individual. It would seem therefore 

 as though the number both of spines and plates may well have 



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Fig. 3. Left side of the model showing superficial muscles and bony plates. 



been a specific character if not an individual or possibly a sexual 

 Variation. 



During the erection of the Yale specimen an admirable op- 

 portunity was offered for another restoration of which I have 

 taken advantage, this time using a scale of one-fifth to reduce 

 still further the margin of error. The model is based not alone 

 upon the proportions and position of the various bones as in the 

 mounted skeleton but also upon etu dies of the individual bones made 

 with a view of indicating thereon the attachments of the various 

 skeletal muscles of the body and limbs. In this work a small 

 alligator was dissected and used for comparison, and a specimen 

 of Sphenodon (Hatteria) as well. I was also aided by the admirable 

 work of v. H u e n e on the musculature of Plateosaurus erlen- 

 bergiensis (Die Dinosaurier der Europäischen Triasformation, Jena, 

 1908) as well as Haughton's work on the muscular anatomy 



