328 ROOT OF PENTACRINITE. 



succession of teeth, set at minute intervals from one another^ 

 and locking into the interstices between corresponding teeth 

 on the surface of the next vertebrae, they are so disposed as 

 to admit of flexure in all directions, without risk of disloca- 

 tion.* 



As the base or root of Pentacrinites was usually fixed to 

 the bottom of the sea, or to some extraneous floating body, 

 the flexibility of the jointed column, which forms the stem, 

 was subservient to the double office, first, of varying, in 

 every direction, the position of the body and arms in search 

 of food, and secondly, of yielding, with facility, to the course 

 of the current, or fury of the storm, swinging, like a vessel 

 held by her cable, with equal ease in all directions around 

 her moorings. 



The Root of the Briarean Pentacrinite was probably 

 slight, and capable of being withdrawn from its attach- 

 ment.! The absence of any large solid Secretions, like 



* The ranges of tubercles upon the exterior surface of each joint in the 

 fragments of columns, PI. 52. Figs. 7. 9. 11. mark the origin and insertion 

 of muscular fibres, by which the movement of every joint was regu- 

 lated. At every articulation of the vertebrae, we see also the mode in which 

 the crenated edges lock into one another, combining strength with flexi- 

 bility. In PI. 52, Figs. 11. and 13, the Vertebrse (d.) present five lateral 

 surfaces of articulation, whereby the sidc-;\rms were attached to the vertebral 

 column at distant intervals, as in the Pentacrinus Caput Medusae, PI. 52, 

 Fig. 1. 



The double series of crenated surfaces, which pass from the centre to the 

 points of each of the five radii of these star-shaped vertebrae, PI. 62. Fig. 6. 

 to 17.; and PI. 53. Figs. 9. to 13, present a beautiful variety of arrangements, 

 not only in each species, but in different parts of the column of the same 

 species, according to the degree of flexion which each individual part re- 

 quired. 



t Mr. Miller describes a recent specimen of Pentacrinus Caput Medu- 

 sa;, as having tlie joints next to the base partially consolidated, and ad- 

 mitting but little motion, where little is required; but higher up, the 

 ioints bcuome thinner, and are disposed alternately, a smaller and thinner 

 joint succeeding a larger and tliicker, to allow a greater freedom of mo- 

 tion, till near the apex this change is so conspicuous, that the small ones 

 resemble thin leather-likc interpositions. He also observed traces of 



