The Vertebrate Skeleton by Sidney H. Reynolds

Author:Sidney H. Reynolds [Reynolds, Sidney H.]
Language: eng
Format: epub
Published: 2016-07-30T00:00:00+00:00

Fig. 58. A, dorsal and B, ventral view of the pelvis and sacrum of a Duck (Anas boschas ).

1. ilium.

4. pectineal process.

2. ischium.

5. lumbar vertebrae.

3. pubis.

6. true sacral vertebrae.

The Sacrum.

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.

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