The =sixth= cervical vertebra has the following distinctive features: It is shorter and wider than the fifth. The =arch= is large, especially posteriorly. The =posterior articular= processes are shorter, thicker and further apart; they are connected with the anterior ones by a thick ridge. The =spinous process= is less rudimentary; it is half an inch or more (ca. 1.5 cm.) in height. The =transverse processes= have three branches; the third part is a thick, almost sagittal plate, which forms with its fellow and the body a wide ventral groove on the posterior part of the vertebra; the other branches correspond to those of the typical vertebræ, but are short and thicker. The =foramen transversarium= is large; below its posterior end is a fossa. The =ventral crest= is small and is less prominent posteriorly. The third branch of the transverse process and the fossa are sometimes absent on one side. The =seventh= cervical vertebra is readily distinguished by the following characters: It is =shorter= and =wider= than the others. The =body= is flattened dorso-ventrally and wide, especially behind; here it has a =demifacet= on either side for articulation with part of the head of the first rib. The =arch= and its =notches= are large. The =anterior articular processes= are wider and longer than the posterior pair. The =spinous process= is an inch or more (ca. 3 cm.) in height. The =transverse process= is undivided, and has no foramen transversarium. The ventral crest is replaced by a pair of tubercles. In some specimens a large foramen transversarium is present on one side or (rarely) on both. [Illustration: FIG. 9.—ATLAS OF HORSE, ANTERIOR VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ] [Illustration: FIG. 10.—ATLAS OF HORSE, POSTERIOR VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ] THE ATLAS This vertebra is decidedly atypical in form and structure. The body and spinous process are absent. It has the form of a strong ring, from which two curved plates, the =wings=, project laterally. The ring incloses a very large vertebral foramen, and consists of two =lateral masses= connected by =dorsal= and =ventral arches=. The =lateral masses= (Massæ laterales) present two deep oval =anterior articular cavities= (Foveæ articulares craniales) which receive the occipital condyles; they are separated by a wide notch above and a narrow one below. The outer margin is also notched, and a triangular non-articular depression cuts into the inner part of each cavity. The =posterior articular surfaces= (Facies articulares caudales) are somewhat saddle-shaped; they are confluent on the ventral arch below, but are widely separated above, and do not conform in shape to the corresponding surfaces of the axis.