38 Field Columbian Museum — Geology, Vol. II. 



few arches that were recovered complete, or nearly so, from different 

 parts of the series, the restoration of the intervening parts of the 

 series has presented few difficulties. 



The spines decrease very slightly in height, in breadth and in 

 thickness. Anteriorly they are directed somewhat backward, but 

 soon become quite vertical in position. In the posterior cervical and 

 anterior dorsal region the spines present a much larger, oval and 

 truncate extremity for ligament or cartilage; this surface measures 

 from twelve to fifteen millimeters in width in some of the posterior 

 cervicals. In the posterior dorsals the extremity is narrow— three or 

 four millimeters in width. The first diapophysis* is small, for the 

 attachment of a small, short rib, and is situated low down on the 

 pedicle, t close to the sutural surface. The next is much stouter and 

 longer, for the attachment of a long and strong rib. The next two or 

 three ascend progressively on the pedicle, until in the fifth the upper 

 margin of the root is above the plane of the anterior zygapophyses. 

 They retain this position throughout the series, the last two or three, 

 only, descending toward the centrum. The diapophyses have ac- 

 quired their greatest length by the sixth or seventh, and are directed 

 upward and outward. In the articulated skeleton there is a deep 

 costo-spinal groove on either side. The zygapophyses are largest 

 and stoutest in the posterior cervical region, decreasing gradually in 

 size, and becoming obsolete at the base of the tail. Throughout the 

 dorsal region they are but slightly cupped, and are directed dorsad 

 and ventrad, at only a slight angle from the median plane. There 

 are no indications whatever in any region of a zygosphene. The 

 centra throughout this region were more or less crushed in the 

 specimen, but seem to be very uniform in character. Their size is 

 but very little different from that of the posterior cervicals, their 

 length no greater; the venous foramina on the ventral side become 

 gradually more remote from each other. 



Some of the dorsal ribs were so badly decomposed that they could 

 not be recovered from the matrix; others were so intermingled with 

 other bones that they could not be removed entire. The larger part, 

 however, have been recovered and restored nearly to their living 

 condition. The anterior long ribs are flattened, with an expanded 

 head, only moderately curved and with the distal extremity only a 

 little attenuated, the cartilaginous continuation evidently of some 



*Baur (Anatom. Anzeiger ix. No. 4, 1893, p. 120) would restrict this term to the process bearing 

 the head of the rib in the Stapedifera. 



tSeeley has proposed to call these vertebra; in which the rib is ascending from the centrum, 

 pectorals. 



