The Cocci-3c c), the huckie, or whistle bone (named from its supposed resemblance to a cuckoo's bill, from motocvt, Gr.; Os coccygis, Lat. ; i'Os coccyx, Fr. ; das Steissbein, or Schwanzbein, Germ.), is an appendage to.the apex of the sacrum, and terminates the spinal column inferiorly.
It forms the posterior boundary of the lower part of the cavity, and inferior outlet of the pelvis, assisting to complete its walls, to sustain its contents, and to attach some muscles of the leg and perineum. Jts position is oblique from behind, forwards and downwards, but being normally movable on the sacrum, it yields to pressure in both ways. It is usually composed of four, rarely five pieces or tu bercles, which are generally, but not always, soldered to each other, and diminished in size and completeness downwards. When in one piece, it presents a tapering, elongated, knob bed appearance with an anterior and posterior surface, tvvo lateral borders, and a base and apex. The base presents a plane, oval, arti cular surface (a), corresponding to the apex of the sacrum, with which it is articulated, and sometimes ankylosed. Behind this, on
each side, projects upwards and backwards a cornuated process (b), tipped with an ellip tical articular facet, directed upwards and forwards, to articulate with the inferior sacral horns. Below these, the borders commence, presenting three alternate notches (e), and tubercular projections (c), of which the first are much the largest, and complete the sacro coccygeal foramina. The borders are ter minated by a knobbed, sometimes bifurcated apex, and give attachment to the sciatic liga ments, and some muscles (d). The first two of these notches are converted into holes by ligaments, for the passage of the posterior branches of the fifth and sixth sacral nerves. The anterior surface is slightly concave longi tudinally, and smooth, to support the rectum. It has transverse markings, similar to the sacrum. The posterior surface is correspond ingly converse and rough, to attach ligaments and muscles.. The internal structure of this bone closely resembles that of the sacrum.