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



Sacral Index. 



Ross seal . . . . .108 



"Weddell seal . 102-9 



Leopard seal . . . . 114'8 



The caudal vertebrae were ten in number. The posterior six were represented by 

 elongated bodies alone the last being cartilaginous. The 1st possessed, in addition to 

 the body, a definite neural arch terminating above in a rudimentary spinous process. 

 The laminae in the 2nd did not unite superiorly, so that the neural groove was not con- 

 verted into an arch. The third possessed on each side of its body rudimentary laminae. 

 The bodies of the first four caudal vertebrae were keeled on their ventral aspect. The 

 sternum was incomplete, two segments being awanting. Their articulations could not 

 be made out definitely, so I refrain from describing them. 



Ribs. 



The ribs were fifteen in number on the right side and fourteen on the left, this anomaly 

 being explained in connection with the thoracic vertebrae. The 1st, 12th, 13th, 14th, 

 and 15th ribs possessed a single facet each on their heads for articulation with the 

 corresponding vertebrae. The 2nd to llth inclusive possessed two facets separated by 

 a distinct ridge. The 1st to 12th ribs inclusive possessed well-defined necks, while the 

 1st to 13th showed an oval concavo-convex facet for articulation with the corresponding 

 transverse processes. In the anterior series of ribs was a slight depression, in some a 

 roughness, on each side of the articular surface of the head, for attachment of ligamentum 

 conjugale costarum described by Sir WILLIAM TURNER (CJiallenger Reports, vol. xxvi., 

 Report on Seals, p. 14). The shafts of the ribs were slightly curved, the most pro- 

 nounced curvatures being observed in the 2nd, 3rd, and 4th, while the greatest in 

 length were the 8th and 9th. The last rib on the right side possessed a head with an 

 articular facet, no neck, and a feeble shaft. Its length was 127 mm. 



The Fore- Limb. 



The scapula presented the well-marked sickle shape so characteristic in the Phocidae. 

 The anterior and superior or vertebral borders were convex and thin, the inferior or axil- 

 lary was concave and rounded. On the axillary border at junction of lower and middle 

 thirds in the Weddell and leopard seals was a prominent ridge for muscular attachment. 

 No such ridge was present in the Ross scapulae. The dorsum scapulae was divided into 

 a pre-spinous and post-spinous area by a feeble spine. This spine was relatively longer 

 than in the Weddell and leopard seals, but not so well developed. The pre-spinous area 

 was concavo-convex, the post-spinous was flat. There was no acromion process, but in 

 the Weddell and leopard seals this was present although feeble. The coracoid process 

 was rudimentary and projected forwards, measuring from the bottom of the shallow 



(ROY. soc. EDIN. TRANS., VOL. XLVII., 194.) 



