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



Posterior Extremity. — The extreme length of the femur in the adult male from the 

 Messier Channel (jSTo. 3) was 112 mm. The head was smooth and without a fossa for 

 the ligamentum teres ; the neck was stunted, the great trochanter was well marked, 

 and with a shallow digital fossa for the obturator muscle ; the small trochanter was a 

 distinct tubercle, of no great size ; there was a faint posterior intertrochanteric line, 

 a very feeble anterior intertrochanteric line, but no trochanter tertius. The shaft was 

 broadened laterally, though not so much as in Leptonychotes and Macrorhinus ; its 

 inner lateral border was almost straight, its outer lateral border slightly concave, 

 differing therefore from the other two genera, in which, more especially in Leptonychotes, 

 these borders were markedly concave ; though the posterior surface was flat the 

 anterior was slightly convex. A rough ridge passed down the inner border of the bone 

 towards the posterior surface, which apparently represented a linea aspera. The external 

 tuberosity was more prominent than the internal, and they were both grooved ; the 

 outer groove being for the tendon of the popliteus. The patellar articular surface 

 was not hollowed from side to side, and was convex from above downwards ; it was 

 so large as to occupy almost the whole of the front of the lower end of the femur, 

 whilst in Macrorhinus and Leptonychotes it occupied only about the middle third of 

 that part of the bone. This surface was prolonged downwards and backwards so as to 

 be continuous with the internal condylar articular surface, but was separated from the 

 external condylar surface by a narrow groove ; the condylar surfaces were situated on 

 the back of the lower end of the bone, and were separated from each other by an 

 intercondylar fossa. The inner condylar surface was concave from side to side, whilst 

 the outer was convex. In Arctocephalus gazella the femur was only 93 mm. long, and 

 much more slender than in the Messier Channel seal, and this indeed was a character 

 which distinguished all the bones of the hind limb ; the trochanter minor was absent 

 even in the most fully ossified of the two skeletons, in which the head was united to 

 the neck of the bone. The patellar articular surface was continuous with the inner 

 condylar articular surface, but was separated from the outer by a narrow groove, to 

 which the adipose ligament was attached as well as to the intercondylar fossa. The 

 outer border of the shaft of the femur was more concave in Arctocephalus gazella than 

 in Arctocephalus australis. 



The patella was 28 mm. long, and in both species of Arctocephalus had an articular 

 surface transversely elongated and slightly concave from above downwards ; its cutaneous 

 surface was elongated superiorly into a strong tubercle, whilst lower down the bone 

 was flattened, so that whilst the upper end of the bone was 18 mm. in antero-posterior 

 thickness, the lower end was only 10 mm. 



The tibia was 235 mm. long in the Messier Channel adult male. Its superior surface 

 was divided into two articular facets with a rough groove between them, and the outer 

 facet was wider than the inner. The ligamentum patella? was attached to the front 



