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



According to Geryais and Alix,^ the component elements of the tarso-metatarsal bone 

 are recognisable as distinct and separate entities, even to the end of foetal life in the 

 Penguins. These bones therefore unite with one another at a relatively later date in the 

 Spheniscidse than in the majority of birds. Indications of the original composition of the 

 metatarsal portion of this bone by the union of three elements are distinct enough in the 

 majority of birds by reason of the independence of their lower extremities, but in none, 

 so far as I know, are the shafts of the metatarsal bones separated by the well-defined 

 grooves met with in the Penguins. In none, moreover, with perhaps one exception, is 

 the tarso-metatarsus at once so broad and so short as in the Penguins. As shown by 

 Brandt,^ the tarso-metatarsus of the Frigate Bird resembles that of the Penguins in its 

 shortness, but differs in being relatively narrower, as also in the fact that while in the 

 Penguins the grooves between the second and third, and thii'd and fourth metatarsal bones 

 are well defined, only one, and that the groove between the third and fourth metatarsals, 

 is clearly pronounced in the genus Fregata. 



II.— ARTHROLOCtY. 



The ligaments which connect the various bones of the trunk in the Penguins do not 

 differ from those of other birds. 



The modifications in form of the bones of the wing, however, and the slight amount 

 of motion permissible between the difterent segments of that organ in the Penguins, are 

 accompanied by certaia modifications in the form and mode of attachment of the ligaments 

 connecting the separate bones which it may be as well to refer to shortly. 



Ligaments of the "Wing. 



The shoulder joiat is surrounded by a capsular ligament similar to that of other 

 birds. 



Connected with the elbow joint there are two strong internal, and a single external 

 lateral ligament. The former are attached above to the inner side of the distal end of 

 the humerus, and below to the proximal ends of the radius and ulna. The external 

 lateral ligament is attached above to the humerus, and below to the upper end of the 

 radius. In addition to these ligaments, the various muscles of the forearm arising from 

 the humerus, which in the Penguins are reduced to tendinous bands, serve in these birds to 

 strengthen this articulation. The capsule of the joint is completed posteriorly by the 

 strong ligaments which attach the sesamoid bones to the upper end of the ulna. 



1 Osteologie et Myologie des Manchots, p. 9. 



^ Beitriige zvir Kenntniss der Isaturgeschichte der Vogel, in Memoirs de TAcademie des Sciences, St. Peters- 

 burg, 6th series, 1840, p. 150. 



