Introduction to A nimal Morphology. 1 43 



stiicke, Meyer), each made of two segments (Epiphyses), 

 uniting by a median suture. Between each jaw and its neigh- 

 bour, along the base of the pyramid, lie flat radial pieces 

 (rotula, Schaltstiicke, Meyer), forming a fixed basis for the 

 separate motions of the jaws. Parallel to, and deeper then these, 

 are five radial, Y-shaped manubria (Gabel- or Biigelstiicke) 

 attached within to the middle notch at the central end of the 

 radial pieces, externally projecting freely by their forked ends 

 between the jaws ; each of these is also double, consisting of 

 an inner and outer segment, united by a suture. In the axis 

 of each jaw, between its segments, is a long, curved tooth, 

 whose tip projects as a hard, enamel-coated, chisel-like point, 

 and the basal end is fibrous, asbestos-like. There are thus 

 forty segments in this " lantern ;" five teeth ; five jaws, each 

 of two segments ; five radials ; five inter-radials, each of two 

 pieces ; and five manubria, each likewise double. The 

 muscles to move the apparatus are: — i. Five intermaxillary, 

 transverse fibres to approximate the jaws from the opposed 

 surfaces of each jaw to its neighbours {Interpyramidales). 

 2. Five intermanubrial clear bands, forming a pentagon on 

 the base of the jaws, for approximating the manubria. 3. Five 

 pair of dilatatores orificii dc?itiiwi, which can also retract the 

 whole apparatus, arising two from each auricle, and attached 

 to lateral grooves at the apex of the jaws. 4. Comminu fores 

 cibonim, also five pairs arising from the interambulacral 

 margin, and passing upwards and inwards, narrowing to the 

 inter-radial arches. A fine muscle is described by Valentin 

 at the base of each tooth, but I have not found it. From 

 each inter-ambulacral space to the outer end of each manu- 

 brial fork stretches an oblique ligament, which has a few 

 smooth muscular fibres in its origin : besides these ligamenta 

 externa obliqua, there are ligamenta externa recta, thin 

 vertical membranes from the auricles to the inner end of the 

 manubrium. The dental apparatus in Cidaridas diff"ers from 

 that of Echinus, above described, as the epiphyses do not 

 unite mesially to form inter-radial arches, but are ankylosed 

 to the radial pieces. In Laganum the jaws are unsymme- 

 trical. 



The pharynx is pentagonal, narrowing to the 



