Anatomy of the Proboscideal Nerve in the Proboscis of the African Elephant (Loxodonta africana)

Abstract

The elephant proboscis (i.e., trunk), a unique muscular organ formed by the combined narial and upper lip region, is a complex muscular hydrostat adapted for a multitude of functions, including grasping, holding, and transporting objects, siphoning, holding, and spraying water, and communication. The proboscis has previously been described as containing tens of thousands of muscle fascicles, each working individually to help bend, curve, and curl the trunk in all directions at any point along its length. Although the muscular system of the proboscis has previously been described in some depth, the unique nervous innervation of the proboscis has been given minimal attention. Here, the previously frozen head of an adult female African elephant (Loxodonta africana) is dissected to investigate the anatomy of the neuromuscular anatomy of the proboscis in more depth. In addition to the complexity of interlacing muscle fascicles and the integrated connective tissues, we identified the proboscideal nerve, a large, 2.5 to 3 centimeter thick nerve that is unique to elephants. The proboscideal nerve is made up of the combined distal nerve fibers of the infraorbital branch of the maxillary nerve (CN V3) and zygomatic branch of the facial nerve (CN VII). Specifically, as the infraorbital branch of the maxillary nerve (carrying sensory innervation) exits the cranium through the infraorbital foramen, the zygomatic branch of the facial nerve (carrying motor innervation) runs along the ventral border of the zygomatic arch and joins the maxillary nerve rostrodorsal to the masseter muscle to form the proboscideal nerve. The proboscideal nerve then travels down the length of the proboscis transmitting small sensory and motor nerve fibers to all muscle fascicles and surrounding skin and tissue. Given this anatomy, fine‐tuned neuromuscular control and coordination of the individual nerve fibers are necessary to control the diverse movements that occur throughout the length of the proboscis. This specialized evolutionary adaptation helped shape a functionally innovative organ that grew, modified, and persisted throughout the course of proboscidean evolution.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.