ART. 18 ON A NEW SKELETON OF DIPLODOCUS GILMOEE 



13 



docns lonc/us as described by Os- 

 born.^^ The vertebrae steadily 

 increase in lenjith from the first 

 to the eighteenth and then di- 

 minish to the hist of the series ; 

 the median cleft on the summit 

 of the spines disappears poste- 

 rior to caudal 8, the diapophyses 

 reduce in size posteriorly, and 

 the lateral cavities extend as far 

 back as the nineteenth vertebra. 



An interesting feature of this 

 tail is the complete coossification 

 of the seventeenth, eighteenth, 

 nineteenth, and twentieth verte- 

 brae into a solid rigid section 

 (see fig. 3) ; and in front of this 

 section caudals 15 and 16 are 

 similarly but less fully united. 

 Coossification of the caudal ver- 

 tebrae in DifJodocus has been 

 previously noted b}^ Hatcher ^'^ 

 in specimen No. 94 of the Car- 

 negie Museum, where the seven- 

 teenth and eighteenth are coossi- 

 fied, and again in Carnegie Mu- 

 seum specimen No. 84, of caudals 

 2 and 3. Holland -" in a later 

 communication points out that 

 more careful study indicates 

 that the coossified vertebrae des- 

 ignated the seventeenth and 

 eighteenth by Hatcher in speci- 

 men No. 94 are Nos. 20 and 21 

 of the series, and he adds the 

 information that Nos. 24 and 25 

 of this same specimen are also 

 coossified. 



The coossification of these tail 

 vertebrae in Diplodocus has 

 been directly attributed to trau- 

 matic causes, but in the National 



" Mem. Amor. Mus. Nat. Hist., vol. 1, 

 pp. 204-209, 1899. 



'*Mem. Carnegie Mus., vol. 1, no. 1, p. 

 30, 1901. 



-""Amcr. Nat., vol. 44, p. 2rj5, 1910. 



FiGUHE 3. — Coossified caudal vertebrae (fif- 

 teenth to the twentieth) of Diplodocus 

 longus. About oue-eleventh natural size 



