646 



ON THE ANATOMY OF THE JAQANAS. 



[May I 7, 



anteriorly. The postacetabular ridge has hardly any median pro- 

 jection ; and the pelvis is widest, dorsally, just behind the antitro- 

 chanters. The plates of bone between the ischia and sacrum are 

 narrower, and the posterior part of the renal fossae less well de- 

 veloped, and more open, in consequence. In all these points these 

 forms thus approach the Limicoline birds. 



There is one other point of interest in the osteology of the Parridse. 

 This is the extraordinary form assumed by the radius in some of the 

 genera. In birds, as a rule, the ulna is a stouter bone than the 

 radius, this last being almost universally a slender cylindrical bone. 

 In Metopidius africanus, as already noticed by M . A. Milne-Ed wards^ 

 as well as in M. albinucha and in M. indicus (as I have been able to 

 ascertain by extracting the wing-bones from a skin), the radius pre- 

 sents the form shown in the drawing (fig. 3), being dilated and 



Fig. 3. 



Wing-bones of Metopidius albinucha, to show the peculiarly modified radius ; 



natural size. 



flattened into a suhtriangular lamellar-like expansion for its distal 

 half. Its superior surface is slightly grooved posteriorly for the 

 tendon of the extensor metacarpi radialis longior muscle. 



This dilated portion forms the margin of the patagial space for 

 its distal portion. A considerable portion of the marginal tendon of 

 the tensor patagii longus is inserted into the radius at the angle of 

 the bone ; the main tendon, however, continues in a groove on 

 the inferior aspect of that bone, a little behind the border, to its 

 ordinary insertion. About half of the peculiar flattened radius is 

 left bare of muscle above, the extensor metacarpi, as already stated, 

 playing over its lower half. Below, the flattened area is largely 

 covered by the fibres of the pronator radii superjicialis, which ex- 

 tend up nearly to the margin of the bone ; below this is the pronator 

 radii profundus, which likewise has an extensive insertion into the 

 lower part of the bone. The margin of the bone, where it is super- 

 ficial, is slightly roughened ; and no doubt the peculiar form of 

 radius is associated with the quarrelsome habits of these birds, this 

 dilated and somewhat scimitar-shaped bone being probably capable 

 of inflicting a very severe downward blow. 



In Parra jacana and P. gymnostoma the radius presents the ordi- 

 nary form; and the same is the case in Hydrophasianus chirurgus. 



In these two genera, it is to be observed, the metacarpal " spur " 

 ■ ' Oiseaux Fossiles,' ii. p. 134. 



