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



pronounced, and overhangs a shallow fossa which indicates the uj^ward limit of the. 

 extensor cruris muscle. The posterior border of the trochanter is rough, and affords 

 insertion to the obturator internus and gemelli muscles. The outer surface of this 

 eminence is likewise rough, and marked by three depressions, into which are inserted 

 from above downwards the gluteus medius, obturator externus, and gluteus minimus 

 muscles. The shaft of the femur is nearly cylindrical, and presents the longitudinal 

 curve usual in birds. A " linea aspera " can hardly be said to exist, the posterior 

 surface of the shaft being almost smooth. On the anterior surface of the shaft an oblique 

 ridse continuous with the anterior border of the trochanter is traceable as far as the middle 

 in length of the bone. It affords origin to the extensor cruris. 



The lower end of the bone is provided with two condyles, of which the internal is the 

 broader. The groove on the outer side of the external condyle for articulation with the 

 head of the fibula is well developed. The intercondyloid surface for the patella is much 

 pronounced. On the posterior surface of the lower end of the femur is a deep recess, 

 which affords insertion to the lower fibres of the adductor magnus, and origin to the outer 

 and inner heads of the gastrocnemius muscle. 



I have observed the following peculiarities in the femur of Aptenodytes, as compared 

 with that of other species -.—First, In Aptenodytes the femur is relatively stouter and 

 more powerful than in other species. Second, In Aptenodytes the internal condyle of the 

 femur does not project beyond that of the external to the same extent as in other species. 

 Hence in Aptenodytes when the lower end of the femur is placed on a horizontal surface, 

 the shaft of the bone is directed nearly vertically upwards, whereas in other species 

 the shaft of the bone is directed obliquely upwards and outwards. Third, In Apteno- 

 dytes the summit of the trochanter projects above the level of the articular head of the 

 bone to a greater extent than in other species, all of which agree with one another in this 

 as weU as in the other points indicated. 



The table on the following page shows the length of the femur in different species in 



inches. 



The Patella. 



The patella (PI. VII. figs. 9 and 10) is of exceptionally large size, and presents a 

 somewhat peculiar form in the Penguins. In form it resembles a wedge, the anterior or 

 sharp margin of which is directed forwards, the base backwards towards the femur. The 

 base of the wedge is broad, deeply concave, and adapted to the pulley-like surface of the 

 lower end of the femur. The outer surface of the bone is for the most part smooth, but 

 presents about its middle a deep and narrow groove which, commencing in front at the 

 middle of the anterior border of the bone, passes obliquely backwards, downwards, and 

 outwards across the external surface. This groove accommodates the tendon of the " am- 

 biens " muscle. The inner surface of the bone is smooth. The upjjer end of the patella 

 is obliquely truncated, and affords insertion to the muscular fibres of the extensor cruris 



