22 



MEMOIES OF THE CARNEGIE MUSEUM 



posteriori}'- it will readily appear that the fulcrum formed by each anterior vertebral 

 articulation would be subjected to successively greater strains during the process of 

 elevation of the skull and that portion of the cervical series anterior to such ver- 

 tebra. In order the better to resist these increased strains not only does the ball and 

 socket of each vertebra successively increase in size, but the zygapophyses expand 

 and the anterior ones, against which an increased proportion of the strain would be 

 directed, are greatly reinforced inferiorly by the development of a second or even 

 third inferior branch of the prezygapoph^'-sial lamiuEe (three in C. 10). These 

 additional laminae extend from the inferior surface of the broadly expanded prezy- 

 gapophyses to the superior surface of the centrum, and are so arranged as to afford 

 the greatest resistance possible to an}^ force exerted from above. In C. 10 the me- 

 dian septum, which in the mid-centi'al region in most of the cervical vertebrae alone 

 separates the pleuro-central cavities, fails, and there is in this vertebra a large vacuity 



Fig. 7. Tenth, eleventh and twelfth cervicals of Diplodocus carnegii. Seen from right side ; one 

 fifteenth natural size. From Xo. 84, Carnegie Museum collections. 



connecting these cavities. Near the lower and posterior borders of the postdia- 

 pophysial cavities there are in most of the vertebrae (absent in C 9) rather promi- 

 nent foramina. In C. 10 these form a vacuity situated above the neural canal and 

 connecting the opposite cavities. The cervical ribs are prominent, bear anterior 

 and posterior branches, and are connected with the transverse processes thus enclos- 

 ing lateral foramina. Their position throughout the entire series is inferior to the 

 centra. 



Eleventh Cervical. — This vertebra is so unlike either the immediately preceding or 

 succeeding vertebrae that if it had been found isolated it would have been unhesi- 

 tatingly referred to a distinct genus. Mr. Coggeshall, however, assures me that it 

 was interlocked with the succeeding, or twelfth cervical. The right side of this ver- 

 tebra is very nearly perfect, the left was badly injured and the zygapophyses and left 

 neural spine have been restored, not as they are shown on its right side, but as rep- 



