168 



molars can be brought to play upon the under concave surface of 

 the beak-shaped internal cusp of the upper molars, the whole thus 

 representing a very complicated cutting and grinding apparatus. 

 In front of the molars the arch of the mandibular teeth lies 

 within that of the maxillary. 



According to the above description, then, the dental formula is 



i 3 pi -Ks 2 -pT 4 1 O 



but as there are certain variations in the skulls at my disposal, 

 and in ignorance of the succession of the teeth, it is possible that 

 this formula may require some modification. 



THE HYOID BONE. 



(PI. YIL, figs. 3 and 4.) 



In one specimen this bone is represented by two flattened rod- 

 like thyrohyals, osseous for the greater part, but cartilaginous 

 at their laryngeal extremities. In front they touch in the middle 

 line, but are not ankylosed. They are joined by a flat, semicircular 

 and cartilaginous basihyal. In another specimen, in which the 

 thyroid had become largely calcified, the thyrohyals were stouter 

 and shorter in front ; these were completely ankylosed, and 

 joined by a semicircular basihyal, as in the other case. 



THE VERTEBRAL COLUMN. 



Atlas (PI. VII., fig. 5, a) free ; neural canal almost circular ; 

 transverse and spinous processes rudimentary. The articular 

 surfaces for the occipital condyles, concave in the dorso-ventral 

 axis, encroach somewhat on the ventral arch, which is furnished 

 with a semilunar facet for the odontoid process of the axis. The 

 posterior arch bears on its hinder surface a small facet for a 

 corresponding surface on the fused spinous processes of the five 

 ankylosed vertebrae which follow. The rudimentary transverse 

 process carries on its posterior surface a triangular facet for a 

 corresponding surface of the axis. 



The five succeeding vertebra? are completely ankylosed, the only 

 indication of the component vertebrae being the intervertebral 

 foramina for the spinal nerves, of which there are four. (PI. YIL, 

 figs. 5 and 6 c.J The fused bodies fornaa bony mass, generally much 

 compressed dorso-ventrally, but having its lateral borders carried 

 considerably downwards and backwards so as to convert the 

 under surface of the mass into a wide shallow groove ; in the an- 

 terior part of this groove there is a slight median ridge. The neural 

 arches are also ankylosed, but their fused laminae form laterally 

 compressed plates, pointing forwards, which are much shorter in 

 an antero-posterior direction than the fused bodies. So also are 

 the spinous processes completely fused into a single tuberculated 



