ECHINODERMATA. 



167 



nected with several bony levers, by means of numerous mus- 

 cles provided for the movements of the whole. These parts we 

 must now proceed to describe seriatim. The teeth (fig. 71, a) 

 resemble, at the part protruded from the mouth, long three- 



sided prisms, and at this point they are extremely hard and brit- 

 tle : each tooth is fixed in a socket passing through the jaw, 

 (fig. 71, e,) from which it projects by its opposite extremity, 

 (fig. 71, a',) that may be called the root of the tooth, where, instead 

 of being of glassy hardness like the point (a) which issues from the 

 mouth, it is flexible and soft, resembling fibres of asbestos, and 

 is covered by a membrane apparently connected with its secretion. 

 The jaws, which thus support and partially enclose these teeth, are 

 five in number : when examined separately, each is found to 

 resemble in figure a triangular pyramid, the external surface 

 (fig. 71, e,) being smooth, and presenting eminences provided 

 for the attachment of muscles ; while the other two sides 

 (fig. 71, b, b^ are flat, and marked with transverse grooves, 

 so as to have the appearance of a fine file. When the five jaws 

 are fixed together in their natural positions, they form a five- 

 sided conical mass, aptly enough compared by Aristotle to a 

 lantern, and frequently described by modern writers under the 

 name of the " lantern of Aristotle." When thus fitted to 

 each other, the two flat and striated sides of each jaw are in 

 apposition with the corresponding surfaces of two others, so that 



