THE SKELETON. 31 



the metacarpal for pollex is always very short, while the other two, united 

 only at their ends, extend the hand, which extension is prolonged by the index 

 digit. Many of the modifications of the skeleton of the wing in birds are 

 extremely interesting, and in studying this part of the bony framework we 

 must be carefid not to overlook certain sesamoidal ))ones that may occnr at 

 the glenoid <ia,\\\y {Ii mni'vo scapul arc) at the elbow; at the carpus (oxjiroftu'iicnn),' 

 and sometimes elsewhere. 



Turning to the pe/rir l/'i/ib, or the skeleton of the leg, or lower extremity, 

 we find it divided into the thigh, made up of \\\e_ffiiinir; the leg, containing the 

 tihia., or more properly ihe'tlhio-tai'svx , and the fhida; the foot consisting of 

 the unusually long mi'tatamaJ hone and the phalanfjfs of pes. Exceptionally 

 the tariio-metatarsxm is very short, as in the Man-o'-War bird (^Frcrjata), while 

 in others the number of digits may be reduced, as in Strut/no, or their posi- 

 tion altered (Picm, the Parrots, etc). Most birds have apatellc in front of 

 the knee-joint and this sesamoid may be double, or it may assume very re- 

 markable form or size, or it may be pierced or grooved for the passage of the 

 tendon of the ambiens muscle; or it may coOssify with the elongated cnemial 

 process of the tibio-tarsus as in Loons and Grebes. Penguins have, and the 

 extinct llesperorniH had, large patellar, while they are absent in Ducks and 

 others. 



The femur has a shaft and two enlarged extremities. Proximally, we 

 find the head, a reduced "neck," and a prominent "trochanter major," while 

 distally, there is to be seen the two large condyles, — an internal and an 

 external one. The shaft of the femur may be straight, slender, and long, or, 

 as in the Loons, it may be comparatively stout, short, curved, and the surface 

 of its shaft roughened by lines, ridges, and tuberosities for muscular insertion. 



Externally, in the skeleton of the leg, occurs the fhula, usually a very 

 slender element. At its proximal end is an enlarged head for articulation in 

 the fibular groove on the back of the external femoral condyle. With the 

 tibio-tarsus, it articulates by a more or less extensive "fibular ridge," below 

 which the bone often becomes rapidly spindle-form, and may terminate in a 

 free needle-like extremity. The fibula may be complete in some birds 

 {Pandion, Snla, and in certain Loons and Grebes), but in them it always fuses 

 to the side and lower extremity of tibio-tarsus. Often it is very short and 

 free, the abbreviation, however, always taking place below the fibular ridge 

 of the main bone of the leg or the tihlo-tarsus. This latter usually has a 

 long, stout and straight shaft with enlarged extremities. Proximally, it arti- 

 culates with the two condyles of the femur, while its head, anteriorly, may be 

 produced upward to a greater or less degree as a prominent cnemial process, — 

 very conspicuous in some birds, as in the Loons and the Grebes; distally it 

 possesses two condyles, placed antero-posteriorly, and articulating, in the natural 



