24 THE VOYAGE OF H.M.S. CHALLENGER. 



was immature the vertebrae had not assumed their adult characters, and various of 

 the processes were probably less strongly marked than would have been the case in 

 a mature animal. As previously stated, the epiphysial plates were not ankylosed to the 

 bodies. 



In all the cervical vertebras, except the 7th, a vertebrarterial foramen was present 

 between the two roots of each transverse process, and in the atlas the neural arch was 

 also perforated on each side. The transverse process of the atlas was a broad plate pro- 

 jecting almost transversely outwards ; that of the axis was short and pointed ; those 

 of the 3rd, 4th, 5th, and 6th were more massive, and ended in two tubercles, that of 

 tbe 7th was a single bar of bone springing from the neural arch. In the configura- 

 tion of its transverse processes Weddell's Seal approximated closely to the Elephant 

 Seal and differed materially from the corresponding processes in Arctocephalus, in 

 which animal they were flattened into broad plates which projected almost vertically 

 downwards, though in the case of the atlas they were elongated downwards and out- 

 wards. The axis was the only cervical vertebra with a prominent spine ; its odontoid 

 process was 19 mm. high, and fused with the body of the axis. The ventral surface of 

 the bodies of the cervical vertebrae had a mesial keel. 



The dorsal vertebras articulated with fifteen pairs of ribs ; the 1st with one and 

 a half, the 11th, 12th, 13th, 14th and 15th with only a single rib on each side, the 

 others with the halves of the heads of two ribs. When only a single rib articulated 

 with the side of the body, it was near its anterior part. The transverse processes were 

 prominent from the 1st to the 10th dorsal, behind which they diminished in size, and 

 were scarcely to be recognised in the 14th and 15th dorsal vertebrae. The spines were 

 feeble. 



In the lumbar vertebras the transverse processes were elongated, and projected 

 forwards, outwards, and downwards. The spines were not very prominent. The body 

 was keeled on its ventral surface. 



The sacrum was represented apparently by only two vertebras, though it is possible 

 that the more anterior of the two caudal vertebras which possessed a neural arch, 

 might in a mature animal be ankylosed with the sacrum. Of the two vertebras 

 which I have regarded as sacral, the first was much the larger, its breadth at the 

 base was 100 mm., and its antero -posterior diameter was 40 mm. It had abroad lateral 

 articidation with the ilium, 47 mm. in its longer diameter, whilst the corresponding 

 articulation of the second sacral was only 17 mm. in its longer diameter. 



Each of the caudal vertebras, except the two most anterior, consisted of an elongated 

 body, without a neural arch, and they diminished in length from before backwards, the 

 terminal vertebra being only 12 mm. long. 



Ribs. — Of the fifteen pairs of ribs, ten articulated with the sides of the sternum. 

 The capitular epiphysis was not in any bone ankylosed to the rest of the rib. The 



