. The structure and life of birds . resemblances where it isdifficult for us to see any has run riot. The larger oftrie two leg bones is the Tibia or flute, the smaller oneis the Fibula or brooch (F, fig. 1, 3). The Acetabulum,as they called the socket of the thigh-bone, is a happiername. Strictly the word means a vinegar-pot, andit is used of any cup-shaped vessel. A birds Ace-tabulum (A, fig. 8) is remarkable. If you look at askeleton in a museum you will see that the cup has nobottom to it. The bottom was formed of membrane, ii SKELETONS OF BIRD AND REPTILE 17 not, as in mammals and most re
. The structure and life of birds . resemblances where it isdifficult for us to see any has run riot. The larger oftrie two leg bones is the Tibia or flute, the smaller oneis the Fibula or brooch (F, fig. 1, 3). The Acetabulum,as they called the socket of the thigh-bone, is a happiername. Strictly the word means a vinegar-pot, andit is used of any cup-shaped vessel. A birds Ace-tabulum (A, fig. 8) is remarkable. If you look at askeleton in a museum you will see that the cup has nobottom to it. The bottom was formed of membrane, ii SKELETONS OF BIRD AND REPTILE 17 not, as in mammals and most reptiles, entirely ofbone, and it has vanished. But ankylosis or fusion isperhaps the most marked characteristic of a birdsLeg. There are the same bones as in the lizards leg,if we could only see them—viz. : Femur (FE, fig. 2)or thigh-bone, Tibia (T), Fibula (F), two rows ofTarsals or ankle-bones (TA), four of the lizards fiveMetatarsals (MT), though of one of the four only thefarther end (MTP fig. 2) remains, and four of his five. Fig. 6.—Hatteria Lizards left hind , 5, digits ; f, fibula; MT, metatarsals; t, tibia; taj, two bones fixed,represents near row of tarsals ; ta-_>, distant row. digits. The Femur has not undergone so muchchange, but the Tibia and Fibula (fig. 3) are verydifferent from the corresponding bones in latter has nearly vanished ; it is a slender, almostneedle-like bone, attached to the side of the Tibia andnot reaching to its farther end. In many mammalstoo the Fibula is but a remnant. The way to makecertain, in the skeleton of any animal whatever, whichbone is the Tibia and which the Fibula, is to imaginethe limb extended, as it is in the lizard, outwards fromthe body ; then the Tibia is praeaxial and the Fibula C 18 THE STRUCTURE AND LIFE OF BIRDS chap. postaxial. But if we look for the birds tarsals theyare not to be seen. The disappearance of the nearerrow is to be accounted for in this way : the bone wehave just called the Tibia
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