MCEEITHEEIUM. 



Ill 



with the form of the latter are narrower from side to side than is generally the case, 

 so that the outline of the articulation with the skull is more nearly circular than usual. 

 I'he condylar cups are separated above by a slight emargination of the anterior 

 border of the massive neural arch and ventrally by a somewhat smaller emargination 

 of the ventral bar. The neural arch at about the middle of its length is raised 

 into a very prominent transverse ridge, from the anterior border of which smaller 

 and less prominent ridges run outwards and forwards to the upper angles of the 

 condylar cups. Behind the ridge the surface of the arch slopes smoothly down to its 

 concave posterior border. Externally to the outer ends of the above-mentioned 



Text-fig. 43. 



Part of right ramus of an immature mandible of Mceritherium lyonsi, showing pm. 4 in situ beneath mm, 4. 



f nat. size. 



lateral ridges the arch is perforated obliquely by the foramen for the first spinal nerve. 

 The transverse processes {t.p.) are rather small and are directed upwards and backwards 

 at their outer ends ; they do not appear to be perforated by the vertebrarterial canal. 

 Anteriorly the base of the transverse process is separated from the neural arch by a 

 notch. The nearly flat surfaces for the axis {a.t.) form an angle of about 45° with 

 the axis of the vertebral column; dorsaUy they are widely separated by the neural 

 arch, and ventrally by a much shorter interval occupied by the ventral bar, which is 



