1. pro-atlas. 2. lateral portion of atlas. 3. odontoid process. 4. ventral portion of atlas. 5. neural spine of axis. 6. postzygapophysis of fourth vertebra. 7. tubercular portion of fourth cervical rib. 8. first cervical rib. 9. second cervical rib. 10. convex posterior surface of centrum of fourth vertebra.] THE CERVICAL VERTEBRAE. Counting as cervical all those vertebrae which are anterior to the first one whose ribs meet the sternum, there are nine cervical vertebrae, all of which bear ribs. As a type of the cervical vertebrae the fifth may be taken. It has a short cylindrical =centrum= deeply concave in front and convex behind. From the anterior part of the ventral surface of the centrum arises a short =hypapophysis=, and on each side is a facet with which the lower limb (=capitulum=) of the cervical rib articulates. The =neural arch= is strongly developed and drawn out dorsally into a long =neural spine=, in front of which are a pair of upstanding processes bearing the prominent upwardly and inwardly directed =prezygapophyses=. At the sides and slightly behind the neural spine are a corresponding pair of processes bearing the =postzygapophyses=, which look downwards and outwards. At the point where it joins the centrum the neural arch is drawn out into a short blunt =transverse process= with which the upper limb (=tuberculum=) of the cervical rib articulates. The sides of the neural arch are slightly notched behind for the exit of the spinal nerves. The first or =atlas= vertebra differs much from any of the others, and consists of four quite detached portions, a ventral arch, with two lateral portions and one dorsal. The =ventral arch= (fig. 41, 4) is flat below and slightly concave in front, forming together with two flattened surfaces on the lateral portions a large articulating surface for the occipital condyle of the skull. Its posterior face is bevelled off and forms with a second pair of facets on the lateral portions a surface with which the odontoid process of the second vertebra articulates. The postero-lateral surfaces of the ventral arch also bear a pair of little facets with which the cervical ribs articulate. The lateral portions are somewhat flattened and expanded, and bear in addition to those previously mentioned a pair of small downwardly directed facets, the postzygapophyses, which articulate with the prezygapophyses of the second vertebra. The dorsal portion (fig. 41, 1) is somewhat triangular in shape, and overhangs the occipital condyle. It is often regarded as the neural arch of a vertebra in front of the atlas and is called the _pro-atlas_; but as it is a membrane bone it is not properly a vertebral element.