Comparative Morphological Configuration of the Cardiac Nervous System in Lorises and Galagos (Infraorder Lorisiformes, Strepsirrhini, Primates) with Evolutionary Perspective

Abstract

The detailed systematic morphology and comparative anatomy of the autonomic cardiac nervous system (ACNS) with its surrounding structures were examined in 14 sides of 7 Lorisiformes species (lorises and galagos) to consider its evolutionary differences and similarities to others in the primate lineage. Our detailed descriptions clarified that (1) a family-dependent morphology of the ACNS does not exist although several variations are recognized as common variation in Lorisiformes, (2) the morphology of the ACNS in Lorisiformes is almost consistent regardless of the number of presacral vertebrae and cardiac positions, and (3) the ACNS morphology in Lorisiformes is extremely different from that in New and Old World monkeys, gibbons, and human, specifically in a narrower contribution of the superior cervical ganglion to the spinal cervical nerves, the caudal position and organization of the cervicothoracic ganglion, and the narrower origins of the sympathetic cardiac nerves, although all parasympathetic vagal cardiac branches are consistently present among the primates. Based on these detailed findings, the systematic and evolutionary morphologies of the ACNS are discussed and compared with our previous works. These results suggest the primate ACNS preserves its evolutionary history without modification and specialization by its functional adaptation as seen in the somatic system.