Anatomy of the feeding apparatus of the nurse shark, Ginglymostoma cirratum

The anatomy of the feeding apparatus of the nurse shark, Ginglymostoma cirr atum, was investigated by gross dissection and computer axial tomography. T he labial cartilages, jaws, jaw suspension, muscles, and ligaments of the h ead are described. Palatoquadrate cartilages articulate with the chondrocra nium caudally by short, laterally projecting hyomandibulae and rostrally by ethmoorbital articulations. Short orbital processes of the palatoquadrates are joined to the ethmoid region of the chondrocranium by short, thin ethm opalatine ligaments. In addition, various ligaments, muscles, and the integ ument contribute to the suspension of the jaws. When the mouth is closed an d the palatoquadrate retracted, the palatine process of the palatoquadrate is braced against the ventral surface of the nasal capsule and the ascendin g process of the palatoquadrate is in contact with the rostrodorsal end of the suborbital shelf. When the mandible is depressed and the palatoquadrate protrudes slightly rostroventrally, the palatoquadrate moves away from the chondrocranium. A dual articulation of the quadratomandibular joint restri cts lateral movement between the mandible and the palatoquadrate. The verti cally oriented preorbitalis muscle spans the gape and is hypothesized to co ntribute to the generation of powerful crushing forces for its hard prey. T he attachment of the preorbitalis to the prominent labial cartilages is als o hypothesized to assist in the retraction of the labial cartilages during jaw closure. Separate levator palatoquadrati and spiracularis muscles, whic h are longitudinally oriented and attach the chondrocranium to the palatoqu adrate, are hypothesized to assist in the retraction of the palatoquadrate during the recovery phase of feeding kinematics. Morphological specializati ons for suction feeding that contribute to large subambient suction pressur es include hypertrophied coracohyoideus and coracobranchiales muscles to de press the hyoid and branchial arches, a small oral aperture with well-devel oped labial cartilages that occlude the gape laterally, and small teeth. J. Morphol. 241:33-60, 1999. (C) 1999 Wiley-Liss, Inc.