The =transverse processes= are large and outstanding in the neck, where they form the outer boundary of a ventral groove occupied by the longus colli muscle. In the back they are short and stout, and are characterized by the facets for the tubercles of the ribs. On the first thoracic vertebra this facet is large, deeply concave, and situated almost directly outward from the cavity for the head of the rib; traced backward it becomes smaller and flatter, and gradually comes to lie behind the cavity for the head of the rib, with which it is fused on the last and often also on the next to the last thoracic vertebra. The processes in the lumbar region have a characteristic elongated plate-like form. In the sacral region they are fused to form the wings and lateral parts of the sacrum. In the coccygeal region they are at first of considerable size relatively, but undergo rapid reduction, and disappear at the fifth or sixth vertebra. The cavities for the heads of the ribs diminish progressively in size and depth from first to last. The =mammillary processes= are usually distinct on the fourteenth to the seventeenth thoracic vertebræ. In front of these they blend with the transverse, behind with the anterior articular processes. The length of the vertebral column (including the intervertebral fibro-cartilages) in a horse of medium size is about 260 to 265 cm. (ca. 8 feet 8 inches to 8 feet 10 inches). The relative lengths of the various regions appear to vary most in the neck and back. The table below gives the measurements in centimeters in a trotting stallion of medium size and in an adult Percheron stallion. The percentages are in round numbers. ─────────┬───────────┬─────────── │ TROTTER │ PERCHERON ─────────┼─────┬─────┼─────┬───── Cervical │ 60.0│22.7%│ 74.0│25.4% Thoracic │ 98.0│37.2%│100.0│34.4% Lumbar │ 31.5│12.0%│ 36.5│12.5% Sacral │ 20.0│ 7.6%│ 22.5│ 7.7% Coccygeal│ 54.0│20.5%│ 58.0│20.0% ─────────┼─────┼─────┼─────┼───── │263.5│100.0│291.0│100.0 ─────────┴─────┴─────┴─────┴───── THE RIBS There are usually eighteen pairs of ribs in the horse, but a nineteenth rib on one side or both is not at all rare. Eight are =sternal= or “true” ribs, the remainder =asternal= or “false.” Ribs from different parts of the series vary much in length, curvature, and other characters. We will therefore consider as a type a rib from the middle of the series first, and afterward note the chief serial differences. A =typical rib= has the following characters: