OSTEOLOGY OF ANTARCTIC SEALS. 23 



Dorsal Vertebrae. 



The bodies of the anterior four were keeled, the keel becoming less pronounced as 

 we proceeded from 1 to 4. At the posterior end of the dorsal region, 14 and 15 pre- 

 sented a slight keel, more accentuated in 15 than in 14. The side of the 1st body had 

 one and a half facets ; 2 to 10 inclusive (two half-facets, 11 to 14 inclusive) a whole facet 

 for the corresponding ribs. The 1 5th dorsal vertebra showed a peculiar arrangement ; thus, 

 on the right side of its body a well-marked facet was present for articulation with the 15th 

 rib of that side, while on the left a well-marked plate-like costal process, representing 

 the last rib, projected from the junction of the body and pedicle outwards, forwards, and 

 slightly downwards. It measures 42 mm. in length and 25 mm. in breadth. (See 

 fig. 5.) 



The spines of the dorsal vertebrae were relatively feeble compared with those of the 

 Weddell and leopard seals. They were low, and projected upwards and backwards as 

 far as No. 11 ; while 12, 13, 14, 15 projected upwards. 



The transverse processes of 1 to 10 were prominent and presented rounded facets for 

 articulation with the tubercles of the ribs. In 11, 12, and 13 the transverse processes 

 were feeble but possessed facets. In 14 and right side of 15 they were rudimentary 

 and non-articular, while the character of the transverse process of left side of 15 has 

 already been noticed. From 9 to 15 the mammillary processes were well defined, while 

 accessory processes were faintly marked in 9 to 14. 



Lumbar Vertebrx and Sacrum. 



Each body of the lumbar vertebrae was elongated antero-posteriorly and was keeled 

 on its ventral aspect. The spines were broad and more pronounced than in either the 

 Weddell or leopard seals. The mammillary processes were rounded and directed 

 forwards and outwards. The transverse processes were thin and flat, and curved out- 

 wards, forwards, and downwards. The sacrum was composed of three segments fused 

 together. The ventral surface in its anterior part was broad and flat, with a faint keel, 

 while its posterior part, corresponding to the 2nd and 3rd segments, was protuberant 

 in the centre, concave laterally, where it presented the openings of the two anterior 

 sacral foramina. The posterior surface showed mesially three spinous processes, while 

 the laminae of the three segments were only fused laterally. The fused articular 

 processes were prominent at the junction of S : and S 2 , less so at S 2 and S 3 . The 

 direction of the 1st posterior sacral foramen was horizontally outwards, in the 2nd and 

 3rd upwards and only slightly outwards. Laterally the sacrum presented a definite 

 U-shaped articular surface for ilium, while the interval between the two limbs of the 

 U and the area posterior to it were hollow for ligamentous attachment. The articular 

 surface for the ilium was confined entirely to the first sacral segment. 



(ROY. soc. EDIN. TRANS., VOL. XLVII., 193.) 



