Meeting Abstract

17.5  Tuesday, Jan. 4  The complex construction of the mandibulo-gular wall of the American Alligator HOPKINS, B.A.*; HOMBERGER, D.G.; Louisiana State Univ., Baton Rouge; Louisiana State Univ., Baton Rouge bhopki1@tigers.lsu.edu

The mandibulo-gular wall of the American Alligator includes the skin, superficial fascia, and constrictor musculature. These three layers need to expand coherently to allow the passage of large prey items through the pharynx and upper esophagus. The tissues that comprise each layer show distinct structural modifications for expansion. The skin expands only at the interscale epidermis, which varies its orientation depending on the shape and size of the adjacent scales. The most expandable regions along the mandibular rami form longitudinal grooves that radiate from the orifices of the paired gular glands, whose oily secretion conditions the skin. The least expandable regions are found subtending the larynx and cranial to the shoulder girdle. The fiber direction of the superficial fascia varies from circumferential, to longitudinal or oblique depending on the local expansibility of the skin. The constrictor musculature returns the expanded mandibulo-gular wall to its resting state and consists of three layers. The most superficial M. constrictor colli cervicalis constricts the caudal portion of the gular region and attaches aponeurotically to the osteoderms on the neck. The deeper and more cranial M. constrictor colli intermandibularis constricts the cranial portion of the gular region and attaches caudally to the osteoderms and cranially to the retroarticular process of the mandible. The deepest M. intermandibularis connects the mandibular rami and raises the floor of the mouth. The complementary nature of the constituent tissues in the mandibulo-gular wall illustrates the typical mechanical coherence of a complex system and facilitates the functional analysis of such a system.