The Sand-Grouse constitute an Order closely allied to the Pigeons or Columbae on one hand, the Gallinae or true Game-Birds on the other.
In the Sand-Grouse the toes are fitted for walking, though the tarsi are short and not adapted for continuous exertion. The bill is Galline in character, though small and feeble, having no cere or soft skin over the tarsal half as in the Pigeons. The Sand-Grouse have eleven primaries and no fifth secondary as in the Columbae whereas the Gallinae have only ten primaries but possess a fifth secondary. In all three orders the muscles of the thighs and legs are similar. The flexor perforans digitorum is attached to the flexor longus hallucis by a fibrous vinculum, the former supplying the three front toes, and the latter the hallux or hind toe. The ambiens muscle is present except in a few Pigeons. The femoro-caudal, except in the Peafowl and Turkeys, the accessory femoro-caudal, the semitendinosus and accessory semi-tendinosus are all present; both carotids are present also, except in the Megapodes.
The keel of the sternum is very high and there are usually two notches on each side of the posterior margin, the inner sometimes reduced to a foramen.
The gall-bladder is present, there is a nude oil-gland and the contour-feathers have after-shafts.
Palate schizognathous; nasals generally schizorhinal but very variable; basipterygoid processes present; cervical vertebrae fifteen or sixteen.
The dorsal feather-tract has an interscapulary fork, and the lateral bare tracks extend on the shoulders as far as the base of the neck.
The young of Sand-Grouse differ greatly from those of the Pigeons, being covered with richly-coloured down when hatched, whilst they are able to run at once and, to some extent, feed themselves.
The tarsus is well feathered in all the members of this family, in one genus, Syrrhaptes, even the toes being covered. They are birds of exceptionally powerful flight with comparatively long wings; the tail-feathers number fourteen or sixteen.
Blanford accepted three genera in this family but Pterocles and Pteroclurus* only differ in the shape of their tails, and this hardly seems a generic character in so small a group of birds. I admit only two genera, Pterocles and Syrrhaptes.
Key to Genera.
A.A hind-toe present ; tarsus feathered in front only; toes naked...........PTEROCLES, p. 261.
B.No hind-toe; tarsus feathered throughout and toes also feathered....SYRRHAPTES, p. 273.