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



a similar relation to the external femoral condyle. On the outer side of the latter 

 is situated a concave articular surface for the reception of the head of the fibula. 



The two anterior tibial crests present the usual arrangement. The internal, the 

 more extensive, is sharp and extends along the upper fourth of the bone, while the 

 external, confined to the upper end of the tibia, terminates in a blunt tubercle. Both 

 the tibial crests rise above the level of the articular surfaces of the upper end of the tibia, 

 and are united together by a transverse osseous lamella, to the anterior border of which 

 is attached the ligamentum patellae. Between this lamella and the articular surface of 

 the upper end of the bone is a hollowed surface, which in the recent state afi'ords attach- 

 ment likewise to the patellar ligament. 



The tibial crests, together with the upper portion of the shaft of the bone form the 

 boundaries of a deep groove which afibrds attachment to the extensor longus digitorum 

 muscle. The outer surface of the external anterior tibial crest is likewise deeply hollowed, 

 and allows of the passage downwards of the femoral head of origin of the tibialis anticus 

 muscle. 



The shaft of the tibia is prismatic at its upper third, but lower down the angles 

 disappear, and the shaft becomes more nearly cylindrical in form. 



Close to the junction of the shaft with the lower end of the tibia is a well-marked 

 osseous bar, which bridges over a groove on the anterior surface of the bone. Through 

 the canal thus formed passes the tendon of the extensor communis digitorum 

 muscle. 



The lower extremity of the bone, as usual among birds, is expanded to form two 

 condyles for articulation with the metatarsal bone. Of these the internal is more 

 prominent than the external. The two condyles unite together posteriorly to form 

 a shallow, grooved, pulley-like surface. 



The tibia presents the same form in every species of Penguin. The measurements 

 of the bone are given in inches in the table on the following page. 



The Fibula. 



The fibula of the Penguins agrees with that of the majority of water birds in 

 being relatively longer than in other birds. In the Penguins as a rule it is about 

 four-fifths of the length of the tibia, and tapers gradually from its upper to its lower end. 

 The upper extremity of the bone, as usual among birds, is provided with two articular 

 facets, of which one, on its inner surface, is deeply concave, and articulates with the 

 external condyle of the tibia, while the other, situated on the upper end of the bone, is 

 adapted to the groove on the lower surface of the external femoral condyle. The anterior 

 surface of the upper end of the fibula presents a deep groove, which, passing obliquely 

 downwards and backwards, disappears on the outer surface, half an inch below the 

 upper extremity of the bone. This groove, when the bones of the leg are in position, 

 is continuous with the oblique patellar groove, and lodges the tendon of the 



