The close interplay existing between the neural transmission and some pharmacologic agents made it advisable to consider together in this section the innervation of the choroid and the action of drugs on the vessels of this structure.* I. INNERVATION OF THE CHOROID 1. Extrinsic Nerves The choroid is well provided with branches of the ciliary nerves. These nerves are delicate filaments through which sympathetic, parasympathetic, and sensory fibers reach the eye. In the rabbit the anatomy of the orbital nerves was carefully studied by Peschel.1 A. Sympathetic Innervation. —(a) Anatomic Data: The preganglionic fibers arise in the rostral thoracic segment of the spinal cord. The white rami communicantes carry the fibers to the cervical sympathetic chain. Here they ascend to the superior cervical ganglion, where they synapse around the postganglionic neurons. The postganglionic fibers leave the ganglion through the internal carotid nerve, and they pass by the cavernous