MUSEUM OF COMPARATIVE ZOOLOGY. 



255 



agreed that these forked pieces (/*) are in some way made from the division 

 of an arm-bone on its median line, and the swinging of each half sideways 

 till it meets and is soldered with the corresponding half of the neighboring 



arm-bone. To understand this, an arm-bone must be described in some 

 detail. Each one then is, near the base of the arm, essentially the same as 

 its fellows. Its inner surface (Fig. A) has, above, a broad umbo (1), below 



JTj.C. 



which are two smaller knobs (2) standing on each side of a socket (3) ; still 

 lower, and quite on the sides, are two large depressions (w) for attachment 

 of muscles; above (T) and below (/) are notches for the upper and lowei 



