14 MEMOIRS OF THE CARNEGIE MUSEUM 



sacrals, and anterior caudals they remain subequal in length, increasing somewhat 

 in the mid-caudal region, while the posterior caudals are elongated, rod-like bones 

 without processes. 



The Neural Arches. — Throughout the entire cervical series the neural arches are 

 low. Commencing with the anterior dorsals they increase rapidly in height and 

 give rise superiorly to the broadly expanded diapophysial elements of the transverse 

 processes, which appear as quite prominent features throughout the entire dorsal 

 series. 



The Neural Spines. — These are either paired, as in the cervicals and anterior dor- 

 sals, where they are placed transversely, or single, as in the posterior dorsals, sacrals 

 and caudals. There is no nodal vertebra separating the paired from the unpaired 

 spines, but the latter are gradually derived from the former by the convergence of the 

 paired spines.'' This commences as a fusion in their inner and inferior margins, 

 first noticed near the base of the spines of the second dorsal. This union becomes 

 gradually more pronounced in the succeeding vertebrse until there is formed in the 

 ninth dorsal a simple spine with emarginate extremity and finally results in the 

 tenth and eleventh dorsals and sacrals in the production of a perfectly simple neural 

 spine with no indication of division. The neural spines of the three true sacrals are 

 firmly united into a single, powerful spinous process, which is the highest in the en- 

 tire vertebral column. Posteriorly the division just noticed in the spines of the 

 cervicals and anterior dorsals is partially imitated in the neural spines of the anterior 

 caudals, but never results in anything more than an emargination of the extremities. 

 This is most pronounced in the sixth caudal, where it attains a depth of some four 

 or five inches. It rapidly becomes less distinct in the succeeding caudals and en- 

 tirely disappears in the eleventh and posterior caudals. The sacral spines are the 

 longest in the vertebral column. Anterior to the sacrum the spines gradually de- 

 crease in length and are directed upward and forward. Posterior to the sacrum the 

 neural spines decrease more rapidly in length and are directed upward and backward. 



The Transverse Processes.'^ — These are best developed on the posterior dorsals, 

 where they spring from the point of union of the long neural spines with the neural 

 arches, and terminate in widely expanded diapophyses. In this region the dia- 



7 It is more pi'obable that the paired spines wei-e derived from the simjile by the gradual and increased 

 emargination of the summits of the latter. Thus the simple sjiines should be considered the primitive and 

 the paired the specialized conditions. 



8 There may be some question as to the exact homology of these processes. Osborn has referred to 

 them both as metapophyses and as diapophyses or transverse processes. Considering their position in the 

 anterior vertebrjc I hardly think they can be other than homologous with the transverse jirocesses of mam- 

 malian osteology. 



