HAPLODONTID^E— VERTEBRA OF HAPLODON RUFUS. 575 



more obliquely forward, becomes more and more horizontal, and narrows in 

 the fore-and-aft direction coincidently with its increase in lateral projection. 

 Metapophyses, as distinct as those of the posterior dorsals, continue unchanged 

 in appearance part way through the lumbar series. The long acute ana- 

 pophyses which continue to be given off from the posterior extremities of the 

 "transverse" processes gradually shorten to the 4th lumbar, and are abruptly 

 suppressed on the 5th and 6th, where the " transverse '' process appears as a 

 simple, falcate, acute process, projecting horizontally outward with strong 

 forward obliquity. For the rest, the centra of the lumbars are stouter, with 

 more hour-glass constriction than those of the dorsal vertebrae, and the pinch- 

 ing of their sides develops a lengthwise median ridge on the under side. 

 The spinous processes maintain their laminar character throughout ; they 

 increase both in length and height to the middle of the series, then decrease 

 in length, but continue to increase in height throughout the series ; the 

 anterior ones are perpendicular, as on the last dorsals ; there is a gradually 

 increasing backward obliquity to the end of the series. The zygapophyses, 

 both pre- and post-, rise higher and higher with successive lumbars. The 

 last lumbar is entirely embraced between the anteriorly projecting ilia. 



The sacrum consists of five vertebrae, perfectly anchylosed, yet retaining 

 evident traces of its composition. The two anterior vertebrae are much 

 larger than the other three, which abruptly decrease in size. The former 

 alone join the ilia ; their lateral elements are completely fused with each 

 other and with the centra, forming an indistinguishable mass, the outer 

 roughened surface of which constitutes the sacro-iliac synchondrosis. Their 

 spinous processes are, however, distinct from each other, and from those of 

 the smaller succeeding vertebrae; the spines of which latter are, on the other 

 hand, fused into a continuous ridge, as is also the case with their lateral pro- 

 cesses. There are five pairs of intervertebral foramina on the face of the 

 sacrum, the anterior pair much the largest, the posterior lying between the 

 last sacral and first caudal ; the corresponding apertures upon the convexity 

 of the sacrum are less conspicuous, though still discernible. The osseous 

 ridge denoting the line of fused zygapophyses is plainly traceable ; the pre- 

 zygapophysis of the first sacral bears a distinct facel, for movable articulation 

 with the last lumbar. The sacrum is less than one and a half inches long, even 

 measuring the produced pre-zygapophyses, and therefore much shorter than 

 the ilia, which project far in front of it; it ends opposite the posterior margin 



