THE VERTEBRAL COLUMN. 49 



the parapophysis a strong round ridge runs backward to the posterior end of the centrum 

 separating the concavity already mentioned as being present below the diapophysis from the 

 deeper one beneath the parapophysis. The inferior surface of the centrum of the third 

 [fourth] cervical is flat but narrow, while that of the axis [third cervical] is narrow but deeply 

 excavated, and the atlas [and axis] is broad and comparatively flat in this region. The 

 centrum of the third [fourth] cervical is both broader and deeper than that of either the atlas 

 [and axis] or axis [third cervical], and this is especially true of its posterior extremity. 



The fourth [fifth] cervical is free and not coossified in any way with the third. Its 

 centrum is a little broader and deeper than that of the preceding cervical ; it is concave poste- 

 riorly and perhaps also anteriorly, though I can not be certain as to this since in the two 

 instances in which we have it in position (Nos. 1822 and 1834, Yale Museum) it has not been 

 detached from the preceding vertebra. Since, however, the centra of the immediately 

 succeeding vertebrae are biconcave it is quite probable that that of the fourth [fifth] cervical 

 is also. The rudimentary parapophysis is represented by a round capitular rib facet situated 

 near the anterior extremity of the centrum and midway between its superior and inferior 

 surfaces. There is no well-defined ridge dividing the side of the centrum into superior and 

 inferior concavities. The diapophysis, which in this and all the succeeding presacral vertebras 

 may be considered as alone representing the transverse process, is situated well up on the 

 side of the neural arch, somewhat anterior in its position to that of either of the two preceding 

 cervicals. It is much flattened supero-inferiorly and expanded antero-posteriorly. It is 

 directed outward and upward and presents on the posterior angle at its extremity an articular 

 surface for the tubereulum of its cervical rib. The anterior and posterior zygapophyses are 

 much produced and overhang respectively the anterior and posterior ends of the centrum. 

 The neural spine rises more directly upward than in the preceding cervicals; it is more 

 pointed and not so robust as that of the third cervical. It is much compressed near the base, 

 where its antero-posterior dimension exceeds by several diameters the transverse, but at the 

 summit it is much contracted antero-posteriorty and slightly expanded transversely, the 

 latter diameter becoming the greater at the apex. The neural canal is somewhat smaller in 

 this region of the neck than in the atlas [third cervical], and it is more nearly circular in 

 outline. The inferior border of the centrum is a little broader than that of the third [fourth] 

 cervical and there is a shallow and narrow median concavity which is deepest posteriorly. 



THE FIFTH, SIXTH, AND SEVENTH" CERVICALS. 



The centra of these vertebrae are subequal in length and a little shorter than the centra 

 of the anterior cervicals. These vertebra? do not differ materially from that last described 

 save that the inferior surfaces of the centra are broader and flatter, the capitular rib facets 

 are successively more elevated in the posterior cervicals, and the spines are somewhat broader 

 antero-posteriorly. The transverse processes are slightly more expanded in the posterior 

 cervicals and the tubercular facets face backward and outward, indicating that the cervical 

 ribs were directed backward and a little outward. 



The above description of the cervical vertebrae is based on the type of Triceratops prorsus 

 (No. 1822, Yale Museum), except that of the seventh, which is wanting in that specimen but 

 is present and in its natural position in the type of Triceratops brevicornus (No. 1834, Yale 

 Museum), as are also the preceding cervicals, though not in so good a state of preservation 

 as in No. 1822, in which all the cervicals save the last are present and in an almost perfect 

 state of preservation. 



THE DORSAL VERTEBRA. 



There are fourteen dorsals in the vertebral series of No. 1834, Yale Museum. These 

 are all interlocked b} r their zygapophyses and are united in front with the complete cervical 

 series. The anterior seven dorsals are complete. The centrum of the eighth is injured on 



a Sixth, seventh, and eighth.— R. S. L. 

 MON XLIX — 07 4 



