16 MEMOIRS OF THE CARNEGIE MUSEUM 



the tubercular facets. They are circular in outline, and occupy the extremities of 

 short processes which spring from the sides of the anterior zygapophyses. Com- 

 mencing with the fifth and continuing throughout the anterior dorsals, these facets 

 are sessile and successively occupy less elevated positions. In the fifth dorsal the 

 capitular facet is on the middle of the neural arch, while in dorsals four and three 

 it has shifted down to the centrum and encroached upon the pleurocentral cavities 

 of these vertebree. ■ In dorsals two and one it lies wholly inferior to that cavity, and 

 in the latter vertebrae it is situated quite on the anterior and inferior margins of the 

 centrum. In dorsals three, four, and five the capitular facet is much larger than in 

 the preceding and succeeding dorsals, and instead of being circular is obovate in outline. 

 The Laminx. — These form a rather complicated system of bony plates springing 

 from the external surfaces of the vertebrae. They are quite effective as mechanical 

 adaptations, affording greater strength and increased surface for muscular attachment 

 with a minimum of weight. They are so arranged about the neural spines, diapo- 

 physes, transverse processes, and zygapophyses as to have afforded greatest support to 

 those elements in those directions against which, during the life movements of the 

 animal, there were exerted the greatest strains and stresses. The following nomen- 

 clature is in the main that of Osborn. 



1. Prespinal Laminse. — Rising from the union of the prezygapophyses and ex- 

 tending to summit of the median or single neural spines.^ 



2. Postsinnal Lamina. — Rising from union of postzygapophysial and extending 

 to summit of median or single neural spines. 



3. Horizontal Laminx. — Uniting the zygapophyses of opposite sides medially, 

 and laterally connecting the prezygapophyses, diapophyses and postz3^gapophyses 

 of the same side. These laminse are divided by the diapophyses into anterior and 

 posterior blades. These blades occupy the same horizontal plane in each of the 

 posterior dorsals, but in the anterior dorsals and in the cervicals they are placed 

 obliquely to the longer axis of the vertebree, and instead of occupying the same 

 plane, they meet in the diapophyses and form a widely open letter V. 



4. Prezyga'po'physial Lamina. — Descending from anterior border of paired spines, 

 or diverging from same border of single spines and usually passing through anterior 

 zygapophyses, capitular facets to superior and anterior margin of centrum. Suj)er- 

 iorly they are usually simple, but below the zygapophyses they may be divided into 

 two or three blades as in the anterior dorsals and most cervicals. 



9 This and the next lamina are not present in the paired spines. The laminte referred to by Osborn as 

 present on those spines are the superior blades of the pre- and postzygapophysial laminaj, and not pre- and 

 postspinal laminae. 



