hatcher": diplodocus (marsh) 17 



5. Postzygapophysial Lamina. — Descending from posterior border of paired spines, 

 or diverging from middle of single spines and passing downward through postzyga- 

 pophyses to form posterior border of neural arch. Simple or branched below post- 

 zygapophyses. 



6. Diapophysial Lamina. — Best shown in seventh dorsal, where it rises from the 

 side of the simple neural spine and descends vertically through the diapophyses and 

 continues throughout about one-half the extent of the neural arch. This lamina is 

 divided by the diapophysis into superior and inferior blades. The superior blade is 

 suppressed in the anterior dorsals and in the cervicals. 



7. Pleurocentral Lamina. — Present only in the median and posterior cervicals and 

 anterior dorsals, where it rises upon the anterior and superior border of the centrum, 

 extends downward and backward, crossing and dividing into two parts the large 

 pleurocentral cavities. 



8. Oblique and Intersecting Laminx. — On the sides of the centra and neural arches, 

 the latter usually supporting the zygapophyses. 



The relative prominence and position of these various laminse vary greatly in 

 the different vertebrae. They are most constant in the posterior dorsals. In these 

 vertebrfB the diapophysial and horizontal laminse meet at right angles and intersect 

 one another at a point midway between the top of the neural spine and base of cen- 

 trum and midway between the anterior and posterior zygapophyses. From this 

 point of intersection spring the tahercular or diapophysial rib facets. Thus the trans- 

 verse processes divide the diapophysial laminae into inferior and superior branches 

 and the horizontal laminse into anterior and posterior branches. The anterior 

 branch of the latter divides in the sixth and preceding dorsals and posterior cervi- 

 cals into superior and inferior blades. 



The Vertebral Cavities. 



1. The Diapophysial Cavities. — The different branches of the horizontal and dia- 

 pophysial laminae radiate from the diapophyses in such manner as to form four 

 large and subequal cavities, or pockets, left open externally. These four cavities, or 

 pockets, are quite constant throughout the entire presacral series, and they are es- 

 pecially prominent in the anterior dorsals and posterior cervicals, where, from their 

 position in regard to the diapophyses, they may be dominated respectively as the 

 infra-, supra-, post- and prediapophysial cavities. In these vertebrae- the diapophysial 

 and horizontal laminae have shifted from the perpendicular and horizontal planes 

 they occupied in the postdorsals to oblique positions. 



