hatcher: diplodocus (marsh) 29 



ported inferiorly and superiorly by the diapophysial laminie which present poster- 

 iorly broad, flat and thin plates. Anteriorly and posteriorly the transverse process 

 is supported by the horizontal lamina which in front has two branches. The bifid 

 spines are confluent throughout one third their length. They are supported pos- 

 teriorly by the postzygapophysial laminre, and anteriorly by the prezygapophysial 

 laminae, which at the base of the spine are suddenly deflected and merged with the 

 diapophysial laminte. Median spine low, with distinct pre- and postspinal laminae. 



The Sixth Dorsal. — This differs from the preceding vertebrae in the more elevated 

 and less expanded neural arch, in the bifid spines, which are confluent throughout 

 two thirds their length, and in the more elevated position of , the capitular rib facets. 

 The emargination of the neural spines in this vertebra is 115 mm., or 4 J inches. 

 For successive emargination of spines in dorsals compare figs, in Plate VII. 



The Seventh, Eighth ,_ Ninth and Tenth Dorsals. — The centra in these vertebrae are 

 short, slightly opisthocoelous, with extremities expanded successively less constricted 

 medially. Pleuro-ce'ntral cavities, large and subequal, extending into base of neural 

 arches. Neural arches much restricted laterally and antero-posteriorly, not wider 

 than middle of centra. Capitular facets round and pedunculate, anterior and in- 

 ferior to the small, circular, subequal, tubercular facets. The latter are borne at the 

 extremities of the transverse processes which are more slender and somewhat' less 

 expanded than are those of the anterior dorsals, zygapophyses produced into the 

 diplosphenal articulations. The postzygapophyses are each supported inferiorly by 

 a narrow median lamina and by two diverging oblique laminie. Anterior zj^ga- 

 pophyses supported inferiorly by prezygapophysial laminre and a very strong oblique 

 lamina on sides of neural arches, which also give support to the capitular facets. 

 Neural spines simple, but emarginate in 7, 8 and 9 ; entirely simple in 10. Strong 

 post- and prespinal laminae ; from the external sides and near the bases of these 

 spring the post- and prezygapophysial laminae. Neural spines much expanded 

 transversely by the expansion of the diapophysial laminae, which superiorly are 

 expanded into rather broad plates presenting extensive vertical external rugosities 

 enclosing rather deep posterior and more shallow anterior spinous cavities. The 

 former extend throughout the entire length of the neural spines. Horizontal laminae 

 with anterior blades bifid throughout half their length in dorsal seven, slightly bifid 

 anteriorly in eight, and quite simple in nine and ten. See Plate VI. 



The Eleventh Dorsal. — This, the last in the dorsal series, is greatly modified and 

 functions as a sacral. It is coossified by the centrum mth the true sacrals, but 

 supports a free spine. There is no true sacral rib. The transverse process is rugose 

 superiorly and is greatly expanded laterally and inferiorly into a broad, thin, dia- 



