ELEMENTARY SKETCH OF THE OSTEOLOGY OF BIRDS. 23 



ridge which plays between the heads of the tibia and fibula, 

 is seen upon the posterior surface of the external condyle (e.c.) 

 Though not belonging to the true skeleton it may be noticed 

 that a sesamoid* bone, called the patellajf is usually deve- 

 loped in the tendon of the qvadriceps extensor femorisX muscle, 

 and that this sesamoid may occasionally be double. 



We come now to the second segment of the leg of the bird, 

 which is very characteristic, and which has been modified in a 

 very peculiar manner from the primitive type form. In man 

 and other mammals the lower leg, or leg below the knee, con- 

 sists of two bones, — tibia^ and fihula^^ ; these are succeeded 

 inferiorly by the ankle or tarsus^ composed of two rows of 

 small cuboidal bones placed one below the other. The ankle- 

 joint is always placed between the tibia and the first row of 

 the tarsus. The tarsus is succeeded by a row of five meta- 

 tarsals**, and each metatarsal carries its own phalanges, which 

 are two in number in the great toe {hallux), and three in all the 

 others. With this slight sketch of the bones of the lower leg in 

 man, we shall be able to understand the differences which 

 exist in the leg of the bird. The small bone of the leg or 

 fibula (pi. I., fi.) in birds forms a long slender style 

 placed on the outer side of the tibia (t.) which terminates inferior- 

 ly iu a point, and which is frequently anchjdosed to the latter 

 bone. The larger bone of the leg, the tibia or rather the tibio- 

 tarsusf^ (pi. I. t. pi. IV., fig. 2) is a very characteristic 

 bone. Its proximal end is expanded and produced into a large 

 cnemial^X crest or process (en). Its distal end (as.) is terminat- 

 ed by a rounded pulley-like surface ; above this pulley there 

 is frequently on the anterior surface an oblique bridge of bone 

 (br.) beneath which pass the tendons of the tibialis anticus and 

 of other long extensor muscles of the legs. The distal extre- 

 mity of this bone (as.) in the young bird ossifies from a 

 distinct centre, and. it has been found that this portion really 



* Sesamoid, from (rrjaafxr], Indian corn, applied to nodular osseous tissues 

 developed in the tendons of muscles. 



f Patella, a cap ; in osteology the bone of the knee-cap. 



j Quadriceps extensor — the muscle forming the anterior part of the thigh which 

 extends the lower leg. Its name is derived from its arising from four distinct heads. 



§ Tibia, a trumpet, applied to the large bone of the lower leg, probably from its 

 length and hollo wness. 



II Fibula, the pin of a broach, applied to the small bone of the lower leg. 



% Tarsus, from Tapaos, the flat of the foot: in anatomy the bones forming the 

 ankle joint. 



** Metatarsals, from fiera, after, and rapsos,— the bones which succeed the 

 tarsus inferiorly. 



ft Tibio-tarsus, compounded of tibia and rapiros a barbarous but very convenient 

 word, indicatmg that the bone to which it is applied is compounded of elements 

 from the tibia and tarsus. 



II Cnemial, from Kvrjfxri the bone of the lower leg. 



