SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. 1 25 



forward inclination, in very marked contrast to the spines of the succeed- 

 ing vertebrae. The zygapophyses are of altogether cervical type, but those 

 of the posterior pair are less strongly divergent than in the seventh cer- 

 vical. The transverse processes also are very much as in the latter verte- 

 bra, but are not quite so broad antero-posteriorly and are thicker dorso- 

 ventrally, especially at the distal end, where they are very heavy and 

 rugose. On the ventral side of each process is an oval, concave facet for 

 the tubercle of the first rib. 



Functionally, the first thoracic is, to a certain extent, a part of the very 

 elongate neck, not so much adding to its length, as increasing its flexi- 

 bility and ease of movement. 



The second thoracic resembles the first of most ungulates. The cen- 

 trum is of a shape similar to that of the preceding vertebra, but is smaller, 

 and the wedge-shaped prominences on the dorsal side have coalesced into 

 a low, rounded ridge ; the facets for the rib-heads are very large and the 

 anterior and posterior pairs are quite closely approximated. The trans- 

 verse processes are short and heavy, with facets for the rib-tubercles which 

 are more obliquely lateral than in the first thoracic. The prezygapophyses 

 are of the cervical pattern, while the postzygapophyses have the thoracic 

 character and are placed on the ventral side of the overhanging neural 

 arch. The spine, though incompletely preserved, was evidently higher 

 and heavier than that of the first thoracic, shorter and more slender than 

 in the succeeding vertebrae, and has a moderate backward inclination. 



The following vertebrae of the anterior thoracic region (PI. XVIII, fig. 

 5) have short, wide, somewhat depressed and opisthocoelous centra, grow- 

 ing more compressed and triangular and having flatter faces posteriorly ; 

 the anterior rib-facets are very elongate, but narrow, while the posterior 

 pair are rounder and more deeply concave. The transverse processes are 

 short, but heavy and conspicuous, with prominent metapophyses arising 

 from the dorsal border, and have subcircular, slightly concave facets for 

 the rib-tubercles. The neural canal is small and nearly circular and the 

 pedicels of the neural arch are deeply notched for the passage of the 

 spinal nerves. The neural spines are very high, laterally compressed 

 and broad, so that those of several successive vertebrae are in contact for 

 their whole length, and have a strong backward inclination or even a 

 backward curvature. 



In the anterior thoracic region, the vertebras closely resemble the cor- 



