32 GENERAL fflSTORY OF BIRDS. 



skeleton, with the upper end of the tarso-metatarsus; these condyles are the 

 coossified astragalus of other vertebrates. Hence the propriety of calling this 

 bone the tibio-tarsus. Above them, anteriorly, the shaft is grooved, and may 

 be spanned obliquely across by a delicate osseous bridge, intended to keep in 

 place the tendons of the extensor muscles as they play in the groove. Popu- 

 larly, the next segment of the pelvic limb, or the tarso-matatarsios, is called 

 the leg, though it properlj belongs to the foot, being composed of the three 

 fused metatarsal bones, with which the podal digits articulate distally. In 

 life it is ensheathed in the horny podothecte in most birds, which may be more 

 or less skinny in others. Its upper end is fused with an epiphysis represent- 

 ing the remaining tarsal bones, often being produced backward as a process 

 termed the hypotarsus. In embryo birds, and in some subadults, the metatarsal 

 bones are distinct, while in the Penguins, large apertures remain between 

 them throughout life. The first metatarsal (accessory metatarsal) is a greatly 

 reduced bonelct, usually suspended by means of ligament at the lower posterior 

 aspect of the main bone, and supports the hallux or first toe, when the bird 

 possesses one. The trochlese for the second, third and fourth toes are often 

 more or less separated, and even produced as "trochlear processes." The 

 clefts between them are produced as longitudinal grooves on the shaft above, 

 and in the first groove to the outer side may occur a foramen for the passage 

 of the anterior tibial artery. Game birds of certain genera, {Gallus, etc.,) 

 have a "calcar" on the inner side of the lower third of the shaft of the tarso- 

 metatarsus; it is covered with the horny "spur" in life. Palaviedea possesses 

 two such spurs. 



The tarso-metatarsus is extremely short in the Man o- War h\r A {Fregata), 

 and notably lengthened in the waders and many limicoline forms, and the Sec- 

 retary bird of Africa. In a state of great reduction, it is said that a fifth 

 metatarsal has been found in birds, but it never supports any semblance to a 

 toe. In fact, existing birds never possess more than four toes, of which the 

 hallux has two joints or phalanges, the series throughout increasing one in 

 each case, till we find the fourth toe with five joints. In some Swifts (Cypselus) 

 the number of joints do not exceed three, while in not a few species of other 

 birds the hallux or hind toe is entirely absent. In the Ostriches {Struthio) 

 the second toe is missing, an exceptional case, and even in its fourth toe the 

 joints seem to be on the road toward final disappearance, and in time, were it the 

 fate species not to be exterminated by man, it might, in its descendants, be- 

 come one-toed, as is the modern Horse and other Equidce. The CJwlornis, a 

 passerine bird of Thibet, has nearly lost its, fourth toe, while the hallux may 

 be elevated or the reverse in various birds. Woodpeckers, Cuckoos, and others 

 have one or the other of the outer digits reversed, while in the Osprey, Owls 

 and others such toes are reversible or partly so. Ja^anas and many waders 



