MCERITHEEItJM. 113 



of this column are : — the atlas, the last cervical, nineteen thoracic (in this series there is 

 a gap, one vertebra at least being missing), four lumbars, and four sacrals. 



On the whole, the atlas is like that of M. lyonsi described above, but differs in several 

 minor points. Thus the transverse spinous ridge of the neural arch is voider ; the 

 anterior border of the arch is less concave ; the transverse processes differ slightly in 

 form and are more upturned ; the surfaces for the axis are deeper from above 

 downwards and less extended from side to side. Some of these differences may be 

 merely apparent and the result of abrasion or distortion. 



In the last cervical the centrum bears a fairly well-marked hypapophysial ridge ; 

 its articular ends are oval in outline, the long axis being transverse, and are slightly 

 concave in the middle. The transverse processes are large, rising partly from the 

 centrum and partly from the arch; they are stout, and- somewhat thickened at the 

 obliquely truncated end. The arch is high and is prolonged upwards into a 

 prominent neural spine. There is no trace of an articiilar surface for the head of the 

 first rib. 



In the first thoracic vertebra the centrum is of much the same shape as the last 

 cervical, but the broad blunt hypapophysial ridge is almost restricted to the anterior 

 end. The transverse processes are stout and short, terminating in a deeply concave 

 rib-facet, looking downwards and forwards. The anterior edge of the transverse process 

 is produced into a shelf-like projection of bone, which is continuous internally with 

 the anterior edge of the neural arch and bears on its upper surface the broad and flat 

 anterior zygapophyses. The neural arch is broader than in the last vertebra and the 

 pointed neural spine slopes strongly backwards. There is a slight cup for a rib-head 

 on the upper angle of the anterior face of the centrum, and a mucb deeper and more 

 sharply defined cup on the upper angle of the posterior face. 



The second thoracic is closely similar, but the tubercular facet of the transverse 

 process looks directly downwards instead of downwards and forwards. At the same 

 time the anterior shelf -like projection becomes smaller, and there is the first trace of a 

 tuberosity on the upper side of the end of the process, which becomes larger till about 

 the eighth thoracic. In this vertebra, owing to shortening, the transverse process 

 seems to pass into the metapophysis which is largely developed in the following 

 thoracic vertebrae. 



The following five vertebrae (text-fig. 44) are generally similar, but the transverse 

 processes become shortened and the haemal ridge is wanting. Furthermore, in 4-7 the 

 oval posterior capitular facet [c.f.) becomes very strongly concave and bordered by a 

 prominent rim. In these first seven dorsals the neural spines {n.sp.) are comparatively 

 slender, terminate in a point, and slope strongly backwards. In the eighth dorsal the 

 form of the spine is transitional to the short broad type found in the posterior thoracic 

 region. In this vertebra also the anterior capitular facet is merely a shallow concavity 

 lying beneath and in front of the very short transverse process, which bears a small 



Q 



