On the Nerve Supply of the Eye of Snapping Turtle

Abstract

1. Fine vegetative fibres are found distributed in the chorioidea of the eye of snapping turtle. The fibres come into close relation with the perivascular plexus and probably end in STÖHR's terminal reticula.
2. The nerve fibres supplied to the ciliary and iridic muscles originate in the rather thick parasympathetic fibres from the n. oculomotorius. These fibres do not form the usual motor end-plates, but end in a peculiar net system of fibres showing frequent change in size, which is remarkably similar in structure to the nervous terminal net observed in the paraganglia of mammals. Such a finding suggests that the above muscles are involuntary muscles resembling the heart muscles in function. No sensory termination could be found in the ciliary body and the iris.
3. The nerves coming into the cornea originate in the plexus ciliaris and comprise thick sensory fibres as well as fine vegetative fibres. The vegetative fibres form in the substantia propria corneae terminal reticula which stand in close contact with the corneal cells. The sensory fibres are originally derived from the n. nasociliaris and end in branched terminations beneath or in the anterior corneal epithelium. Nerve fibres ending in the posterior epithelium are not rare either. These too are of sensory nature in all probability.
4. Neither hairs nor glands are found in the eyelids of snapping turtle, but the sensory nerve distribution is not essentially different from that in man. In their skin part, sensory fibres are comparatively abundant. The fibres run up close to the underside of the epidermis and form their unbranched and simple branched terminations there. In the lidmargin with its well-developed stratum papillare and small papillae growing out thence into the epidermis, the sensory fibres are much more abundant than in the skin part and end in simple or sometimes in rather complex branched terminations. In the palpebral conjunctiva sensory fibres are extremely few and form only very simply formed terminations.
5. The conjunctiva bulbi is rather rich in sensory fibres, including some of thick calibre. These fibres usually end in unbranched and simple branched terminations subepithelially, but intraepithelial fibres are not rare either.
6. The third eyelid of snapping turtle contains more sensory fibres than does the human plica semilunaris. These fibres too, as in the conjunctiva bulbi, end either in very simply formed subepithelial terminations or intraepithelial fibres.