Each of the first five vertebrae has a prominent, vertical, abruptly terminated neural spine, and straight transverse processes. The zygapophyses and articulating surfaces at the ends of the centra are well developed. The third, fourth, fifth, and sixth vertebrae have very prominent hypapophyses. The articular facets for the ribs are well marked, those for the tubercula lying at the free ends of the transverse processes, and those for the capitula at the sides of the anterior ends of the centra. The sixth and seventh thoracic vertebrae are firmly fused by their centra and neural arches to one another and to the lumbar vertebrae behind, and by their transverse processes to the ilia. The sixth has its centrum terminated in front by a saddle-shaped articulating surface, and bears a pair of prominent prezygapophyses. Its transverse processes and centrum bear facets for the tubercula and capitula of the ribs respectively. In the seventh vertebra the tubercular facet is wanting. THE SACRUM. [Illustration FIG. 58. A, DORSAL AND B, VENTRAL VIEW OF THE PELVIS AND SACRUM OF A DUCK (_Anas boschas_). 1. ilium. 2. ischium. 3. pubis. 4. pectineal process. 5. lumbar vertebrae. 6. true sacral vertebrae.] The =sacrum= generally consists of seventeen vertebrae fused with one another and with the ilia. Their number may be reckoned from the number of foramina for the exit of spinal nerves. The two most anterior of these vertebrae bear ribs and have been already described with the other thoracic vertebrae. Their neural spines and those of the four succeeding vertebrae are fused together, forming a continuous crest of bone completely united laterally with the ilia. The transverse processes of all these six vertebrae are well developed, but those of the posterior two (fig. 58, B, 5) are much the stoutest. The next three vertebrae have broad centra, but their transverse processes are very slightly developed and have no ventral elements. These seven vertebrae belong to the =lumbar= series. The remaining eight vertebrae have well-developed transverse processes, which in the case of the first three or four are divisible into dorsal and ventral elements. All the dorsal elements are united to form a pair of flattened plates, partially separated by a series of foramina from a median plate formed by the united neural arches. Laterally they are continuous with the ischia. The first two of this series of vertebrae are shown by their relation to the nerves to be the true =sacrals= (fig. 58, B, 6), the remaining six belonging to the =caudal= series. Behind them come the six free caudal vertebrae, succeeded by a terminal piece, the =pygostyle=, formed of a number of vertebrae fused together; this bears the rectrices or tail quills. [Illustration FIG. 59. SKULL OF A DUCK (_Anas boschas_). × 1. A. Dorsal view of the cranium. B. Palatal view of the mandible. C. The Hyoid. For numbers see Fig. 60.] B. THE SKULL.