Anatomical partitioning and nerve branching patterns in the adult rabbit masseter

The masseter muscle is functionally heterogeneous with a complex architecture consisting of multiple tendons and a multipennate arrangement of muscle fibers. In this study, the anatomical partitioning of the rabbit masseter is described on the basis of the tendons of origin and insertion, general partition orientation relative to the zygomatic arch, motor endplate descriptions, and primary nerve branches that innervate these partitions. This work refines previous descriptions of the rabbit masseter and describes 13 anatomical partitions, each with a unique tendinous attachment. In addition, 14 naturally occurring primary nerve branches were identified and found to innervate different regions of the muscle. After correlating the anatomical partitions and the associated neural innervation pattern, it was determined that simple branch order will not adequately define all the neuromuscular compartments in the rabbit masseter.