Detailed comparative anatomy of the extrinsic cardiac nerve plexus and postnatal reorganization of the cardiac position and innervation in the great apes: orangutans, gorillas, and chimpanzees.

To speculate how the extrinsic cardiac nerve plexus (ECNP) evolves phyletically and ontogenetically within the primate lineage, we conducted a comparative anatomical study of the ECNP, including an imaging examination in the great apes using 20 sides from 11 bodies from three species and a range of postnatal stages from newborns to mature adults. Although the position of the middle cervical ganglion (MG) in the great apes tended to be relatively lower than that in humans, the morphology of the ECNP in adult great apes was almost consistent with that in adult humans but essentially different from that in the lesser apes or gibbons. Therefore, the well-argued anatomical question of when did the MG acquire communicating branches with the spinal cervical nerves and appear constantly in all sympathetic cardiac nerves during primate evolution is clearly considered to be after the great apes and gibbons split. Moreover, a horizontal four-chambered heart and a lifted cardiac apex with a relatively large volume in newborn great apes rapidly changed its position downward, as seen in humans during postnatal growth and was associated with a reduction in the hepatic volume by imaging diagnosis and gross anatomy. In addition, our observation using a range of postnatal stages exhibits that two sympathetic ganglia, the middle cervical and cervicothoracic ganglia, differed between the early and later postnatal stages.