320 MECHANICAL CONTRIVANCES IN ENCKINITE. 



The name of Entrochi, or wheel stones, has with much 

 propriety been applied to these insulated vertebrse. The 

 perforations in the centre of these joints affording a facility 

 for stringing them as beads, has caused them, in ancient 

 times, to be used as rosaries. In the northern parts of Eng- 

 land they still retain the appellation of St. Cuthbert's beads. 



On a rock by Lindisfarn 

 Saint Cuthbert sits, and toils to frame 

 The sea-born beads, that bear his name. 



Maiimion. 



Each of these presents a similar series of articulations, 

 varying as we ascend upwards through the body of the ani- 

 mal, every joint being exactly adjusted, to give the requisite 

 amount of flexibility and strength. From one extremity of 

 the vertebral column to the other, and throughout the hands 



ened margin of the wider, a. b.; the outer crenulated edge of the narrower 

 included vertebrs, articulate with the inner crenulated edge of the wider 

 vertebras, which thus surround them with a collar, that admits of more 

 oblique flexion than the plane crenulated surfaces near the base of the 

 column, Figs. 9, 10, and at the same time rendere dislocation almost impos- 

 sible. 



To these is superadded a third contrivance, which still farther increases 

 the flexibility and strength of this portion of the column, viz. that of making 

 the alternate larger joints, b. b. considerably thinner than the larger collai' 

 joints, a. a. 



The figures numbered from 11 to 26 inclusive, represent single vertebrx 

 taken from various portions of the column of Encrinites moniliformis. The 

 joints at Figs. 11, 13, 15, 17, 19, 21, 33, 25, are of their natural size and 

 in their natural horizontal position, and show, at the margin of each, a cre- 

 r.ated edge, every tooth of which articulated with a corresponding depres- 

 sion near the margin of the adjacent joint. The stellated figures (12, 14, 

 16, 18, 20, 22, 24-, 26.) placed beneath the horizontal joints to which they 

 respectively belong, are magnified representations of the various internal 

 patterns presented by their articulating surfaces, variously covered with an 

 alternate series of ridges and grooves, that like tiie cogs of two wheels, arti- 

 culate with corresponding depressions and elevations on the surfaces of the 

 adjacent vertebrse. 



