POSITION OP THE JAANAS. 223 



Myology. 



Parra jacana resembles P. (Metopidius) africana, as recorded by Garrod*, 

 in possessing the ambiens, femoro-caudal, accessory femoro-caudal, semi- 

 tendinosus, and accessory semitendinosus muscles, all well developed t. 

 Their formula is therefore AB . XY J. In both these species the gluteus 

 primus is well developed, covering the biceps superficially towards the 

 median line ; the gluteus quintus is also well developed. As in the Eallidae, 

 and the Gruidse and Eurypyga, amongst the Pluviales, the area of origin 

 of the obturator internus is triangular, as it is also in Hydrophasianus ; in 

 the Pluvialine birds generally it is oval. The two deep flexor tendons of 

 the foot are not at all ossified, but completely blend together some way up 

 the leg in Metopidius, in fact, just below the joint. There is no slip at 

 all to the hallux, as was also found to be the case in Parra africana || 

 and Hydrophasianus by Prof. Grarrod. This is the more remarkable on 

 account of the very large size of the hallux in all these birds. A special 

 tendinous slip to that digit is very frequently present in birds which 

 have a very insignificant hallux indeed ; and I know of no other case of 

 a bird with such a large hallux as that of the Parridae lacking the tendon. 

 This fact would seem to indicate that the Parridaa may have been 

 developed from some form with a more normal-sized foot and a small 

 hallux, which had no special long flexor, the great size of their feet p z g 

 having been developed in accordance with their peculiar habits. p. 642. 



In the anterior extremity the second pectoral arises from nearly the 

 whole length of the sternum ; in all three genera the third pectoral is 

 wanting. The expansor secundariorum is strong and T-shaped, as in all 

 Ralline and many Pluvialine birds. In Parra jacana (as in Hydro- 

 phasianus, according to Grarrod) there is a distinct biceps slip to the 

 patagium, as in all the EallidaB, the Charadriidae, Gruidae, and many 

 other Pluvialine birds. In Metopidius africanus it is apparently absent, 

 the absence being probably correlated with the peculiar expanded form 

 of the radius (to be hereafter described). 



In the wing- membrane the tensor patagii brevis presents a peculiar 

 arrangement, the tendon being completely divided into two portions 

 an inner, more slender, and an outer, stronger one. The former runs 

 on to the fibrous tissue near the superficial origin of the extensor 

 metacarpi radialis longior, and there stops; the latter continues over 

 this last muscle to the ulnar side of the arm, where it is lost in the 

 fibrous covering-tissue adjacent. Before crossing, however, it sends off 

 a short, special wrist ward slip to the superficial tendon of origin of the 



* P.Z.S. 1873, p.641. 



t In Hydrophasianus all these five muscles are also present. 



I Cf. Garrod, P. Z. S. 1874, p. 123. 



Garrod, P. Z. S. 1876, p. 199. || p. z. S. 1875, p. 348. 



