22 MR ROBERT B. THOMSON : SCOTTISH NATIONAL ANTARCTIC EXPEDITION : 



Cervical Vertebrie. 



The bodies of the posterior six cervical vertebrae were keeled on their ventral aspect, 

 the keel being more pronounced in the anterior thau in the posterior series. On con- 

 trasting the bodies of the Eoss seal with those of the Weddell and leopard seal, a 

 great difference was noticed with regard to their length and breadth. If the 4th 

 cervical be taken as a typical vertebra, we find the length index of the body to be : 



In the Ross seal Length 33 48 x 100 



= Index 145 "4. 

 Breadth 48 33 



In leopard seal Length 51 47x100 _j , 90. ig 

 Breadth 47 51 



In Weddell seal Length 38 = Index 100 



Breadth 38 



If these indices be compared with the length -breadth index of the skull, one is 

 justified in saying that the short and broad character of the Eoss skull can also be 

 applied to the bodies of the vertebrae. The neural ring was triangular. A depth- 

 breadth index shows much the same difference as the bodies in the three species 

 contrasted. In the Eoss seal, the index was 35 "1 ; in Weddell seal, 54'5 ; and in the 

 leopard seal, 50. 



The transverse processes in all except the 7th were perforated at their roots by a 

 vertebraterial foramen, and possessed at their extremities well-marked tubercles in all 

 except the 2nd and 7th. The spinous processes exhibited a marked difference in the 

 various vertebras. Thus the axis possessed a massive spine with four well-marked 

 tubercles two anteriorly and two posteriorly. The 7th had a well-marked spine, not 

 bifid ; the 3rd and 4th had only a trace of a spine, while the 1st possessed a well-marked 

 tubercle representing a spine. The 5th and 6th presented fairly prominent spines, bifid 

 a character not shown by either the Weddell or leopard seals. The type-specimen 

 in the British Museum also exhibits this character. The anterior articular processes 

 looked upwards and inwards, the posterior downwards and slightly forwards. 



The atlas has powerful lateral masses supporting anteriorly deeply concave articular 

 surfaces for occipital condyles, while the posterior articular facets for the axis were fiat. 

 The transverse processes were plate-like, and projected outwards and downwards. The 

 lamina was perforated on each side by a foramen for the vertebral artery, which foramen 

 was situated internal to the upper ends of the articular facets for the occipital condyles. 



The axis did not present so well-marked an odontoid process as either the Weddell 

 or leopard seal. On the inferior aspect of the odontoid process was a triangular facet 

 for articulation with the atlas, whilst superiorly it had a small oval facet for articulation 

 with the transverse ligament. The transverse processes were feeble and pointed, whilst 

 their superior roots were mere spicules of bone. The ventral aspect of the body was 

 markedly keeled. 



(ROY. soc. EDIN. TRANS., VOL. XLVII., 192.) 



