The intramandibular linkage in Astatotilapia elegans (Teleostei: Cichlidae): appearance and function of the meckelian cartilage

During expansion of the bucco-pharyngeal cavity in Astatotilapia elegans , the lower jaws depress and follow the movements of the suspensoria (abduction). Moreover, the angulo-articular part of each ramus rotates around its longitudinal axis in such a manner that the retro-articular process moves laterally (= lateral inclination). As a result, a part of the meckelian cartilage undergoes a torsion.
Elastic moduli of the meckelian cartilage are calculated. It is supposed that during adduction of the head parts, the gained strain energy (due to torsion of the cartilage rod) may be sufficient to move the retro-articular process medially (= medial inclination) by means of elastic resilience. The processes are then held in their resting position, closely to the ventral side of the head. Undoubtedly, the meckelian cartilage acts as a spring, preventing passive lateral movements of the retro-articular processes. In this way, the streamlining of the fish-head is improved when the head parts are in an adducted position.