These, together with the thoracic vertebrae, form the skeletal framework of the thorax. Each rib is a curved rod, which at its dorsal end is movably articulated to the vertebra, and at its ventral end is either connected with the sternum, or ends freely. In the dog there are thirteen pairs of ribs, nine pairs of which are directly connected with the sternum, while the remaining four end freely and are known as =floating ribs=. Each rib is obviously divided into two parts, a dorsal or =vertebral part=, and a ventral or =sternal part=. The vertebral portion, which forms about two-thirds of the whole rib, is a flattened, regularly curved rod, completely ossified. Its dorsal end is rounded, forming the =head= or =capitulum=, which articulates with a concave surface furnished partly by the corresponding vertebra and partly by the vertebra next in front. The last three or four however articulate with one vertebra only. A short way behind the capitulum on the dorsal side of the rib is a rounded outgrowth, the =tubercle= or =tuberculum=, by means of which the rib articulates with the transverse process. The portion of the rib between the head and the tubercle is known as the =neck=. The =sternal portion= of the rib (fig. 76) is a short bar of calcified or imperfectly ossified cartilage, about one-third of the length of the corresponding bony portion. The anterior sternal ribs are somewhat more cartilaginous than the posterior ones. The vertebral portions increase in length from the first which is very stout, and has the capitulum and tuberculum very distinct, to about the eighth or ninth; afterwards they gradually diminish in size. The first nine to eleven have the capitula and tubercula separate, afterwards they gradually merge together. THE STERNUM. This is an elongated cylindrical structure lying in the mid-ventral wall of the thorax, and is divided into eight segments or =sternebrae=. The anterior segment, the =presternum= (fig. 76, 1) or =manubrium sterni= is expanded in front; the next six segments, which, together form the =mesosternum= are elongated, somewhat contracted in the middle and expanded at the ends. The last segment or =xiphisternum= (fig. 76, 4) is long and narrow, and terminates in a flattened expanded plate of cartilage. The first pair of sternal ribs articulate with the sides of the presternum, and the remaining pairs between the successive sternebrae. Between the last sternebra and the xiphisternum two pairs articulate. Development shows that the sternum is formed by the union in the middle line of two lateral portions; this can be well seen in the presternum and xiphisternum of the puppy, but no traces of this median division remain in the adult dog. 2. THE APPENDICULAR SKELETON. The appendicular skeleton consists of the bones of the anterior and posterior limbs, and of their respective supports, the pectoral and pelvic girdles. THE PECTORAL GIRDLE.