\Ret`i*nac"u*lum\, n.; pl. {Retinacula}. [L., a holdfast, a band. See {Retain}.] 1. (Anat.) (a) A connecting band; a fr[ae]num; as, the retinacula of the ileoc[ae]cal and ileocolic valves. (b) One of the annular ligaments which hold the tendons close to the bones at the larger joints, as at the wrist and ankle. 2. (Zo["o]l) One of the retractor muscles of the proboscis of certain worms. 3. (Bot.) A small gland or process to which bodies are attached; as, the glandular retinacula to which the pollinia of orchids are attached, or the hooks which support the seeds in many acanthaceous plants.