HAMMER-HEAD 405 
variable of all the toes, and its taxonomic value is very limited. 
In Hesperornis (ODONTORNITHES), the Spleniscide (PENGUIN) and 
STEGANOPODES it is turned forward, and joined to the second 
digit by a web, as is also the case to a certain extent in the 
Colymbide (DivER). In some of the Cypselide (Swirt) all four 
toes are directed forward, but they are free at the base; and in 
certain of the Caprimulgide (NIGHTJAR) and in the Coliidx (MOUSE- 
BIRD) the Hallux is reversible. In the TUBINARES and the “ three- 
toed” WoopPECKERS (Picoides, Sasia and Tiga) it is reduced to 
a small subcutaneous nodule ; and in most LoitcoL®, though visible, 
it is in a scarcely functional condition, while in some of them, as 
Calidris (SANDERLING) and many Charadriide (PLOVER), it is wholly 
absent, as it is also in the Alcidxe (AuK), Otididx (BUSTARD) and all 
the existing RATIT& except Apteryx (Kiwi). In Rissa (KITTIWAKE) 
its condition varies almost individually from being nearly functional 
to absence (see TOES). 
HAMMER-HEAD or HAMMER-KOP, names given in the 
Cape Colony to the Scopus umbretta of ornithology, called by 
HAMMER-HEAD, Scopus wmbretta. 
Pennant and some writers the “Umbre.” This was discovered by 
Adanson, the French traveller in Senegal, about the middle of the 
eighteenth century, and was described by Brisson in 1760. _ It has 
since been found to inhabit nearly the whole of Africa and 
