252 



THE ANATOMY OF VERTEBRATE!) ANIMALS. 



the pubes unite in a median ventral symphysis. Another, not 

 less remarkable circumstance, in the ostrich, is, that the 31st 

 to the 35th vertebras inclusively (counting from the atlas) de- 

 velop five lateral tuberosities. The three middle tuberosities 

 are large, and abut against the pubis and the ischium. In 

 these vertebras, as in the dorsal vertebrae of Chelonia^ the neu- 

 ral arch of each vertebra shifts forward, so that half its base 

 articulates with the centrum of the next vertebra in front ; and 

 the tuberosities in question are outgrowths, partly of the neu- 

 ral arch, partly of the juxtaposed vertebral centra, between 

 which it is wedged. Hence, in young ostriches, the face of 

 each tuberosit}'- exhibits a triradiate suture. 



The upper articular head of the femur is rounded, and its 

 axis is almost at right angles with the body of the bone ; a 

 structure which is not found in ordinary Rexjtilia^ but exists in 



the Igiianodon and other Ornithosce- 

 lida. The shaft is relatively short and 

 thick, and the two terminal condvles are 

 large and elongated antero-posteriorly. 

 A prominent ridge, which plays be- 

 tween the proximal ends of the tibia 

 and the fibula, is apparent upon the 

 posterior and inferior surface of the 

 outer condyle. A similar ridge is 

 faintly developed in some Lacertilia^ 

 and is well marked in the Dinosaurian 

 reptiles. A patella is usually present, 

 but it is sometimes absent, and may be 

 double. 



The fibula of birds is always imper- 

 fect, ending in a mere style below. 

 Generally it is decidedly shorter than 

 the tibia, but it has the same length as 

 that bone in some Penguins. The tibia, 

 or rather tihio-tarsus^ is a highly-char- 

 acteristic bone. Its proximal end is 

 expanded and produced anteriorly, into 

 a great cneniial process (w^hich may be 

 variously subdivided) as in Dinosauria. 

 SVk f^:;?nai\tai The distal end is terminated by a well- 

 view. T., tibia; F., fibula; marked, pullev-like, articular surface 



Cn., cremial process; As~ ,.-,.'.^,.*', ^ • i- t 



astragalus. which IS niclmed somewhat lorwara as 



well as downward. Not unfrequently 

 there is an oblique bar of bone on the anterior face, just above 

 the pulley, beneath which the long extensor tendons pass. 



A B 



F O. 87.— The right tibia and 



