Pl. -a. [L., a walk, avenue; f. ambulā-re to walk.] An ‘avenue’ or double row of pores for the protrusion of the ambulacral tubes or tube-feet, of which five series radiate from the apex of an echinoderm.
1837. Penny Cycl., IX. 259/1. Species [of Echinidæ] whose ambulacra are petaloid, going from a centre…. This section is divided into subsections, according to the depth of the ambulacra.
1877. Huxley, Anat. Inv. Anim., ix. 568. At its apical extremity the ambulacrum is composed of only two small ossicles which meer in the middle line.
