Supplementary Study on the Innervation of the Human Pia Mater and Plexus Chorioideus

Many proper nerves are found beside the perivascular nerves running along the blood vessels, in the pia mater covering the human brain stem. The latter consist of a small number of vegetative fibres and a large number of sensory fibres, and originate in various brain nerves. The sensory fibres seemingly originate in the rr. meningei of the n. trigeminus in the most part. The proper nerves form rather complex plexus by irregular arrangement of nerve bundles of various size. In the medulla oblongata they are particularly well-developed in the pia of the dorsolateral side and in the mid-brain in the pia of the ventral side of the crura cerebri. The vegetative fibres in the nerve plexus come into anastomosis with the perivascular plexus here and there.The vegetative fibres end always in STÖHR's terminal reticula in the pia mater too, particularly in typical formation around the arteries. Some terminal reticula are formed in the connective tissue too, independent of the blood vessels, especially in good formation in the ventral side pia of the mid-brain. Hardly any nerve cells as allegedly found in the pia mater could be observed in my study.Sensory terminations are said to be found around the blood vessels in the pia mater (STÖHR), and I succeeded in endorsing their existence. The terminations were found, however, to be very simple-unbranched or simple branched terminations-none of the complex type being found.In the connective tissue of the pia mater, many sensory fibres are found ending independent of blood vessels. As their terminal types I found firstly unbranched and simple branched terminations, either with their terminal fibres running winding or looping courses while showing change in size or running comparatively straight courses showing little change in size. The former looping type is found in the pia of the medulla oblongata on many occasions, while the straight type is prevalent in the pia of the mid-brain. It is of some interest that terminal fibres often run into the limit layer of the brain before ending.Secondarily glomerular terminations are pointed out, which comprise the complex type of the terminations with their terminal fibres running looping courses. These are particularly frequent in the medulla oblongata, are non-capsulated and mostly end in the somewhat dark staining plasmodium containing specific cell nuclei. These glomerular terminations can be again classified into the subtypes of the simple and the complex.In my preparations of silver impregnated pia mater, unbranched or simple branched terminations sending in end-knobs or end-bodies (STÖHR) were found only extremely rare indeed. Nor could I observe sensory terminations of various forms having terminal reticula of sensory nature (STÖHR).Nerve bundles are found penetrating into the plexus chorioideus ventriculi IV too. The number of these bundles, however, was found to be very small, in disagreement with what has been reported by some past researchers. Beside the perivascular plexus, proper nerves are found here too, but these are not at all well developed, although the vegetative fibres form clear-cut terminal reticula here too. Nerve cells are said to exist also in the plexus chorioideus, but throughout my study, I could not find any of them.Sensory fibres are found running into the plexus chorioideus as in the pia mater, but in number, these are very small. Their terminations are very simple in construction, limited to unbranched and simple branched terminations formed in the vicinity of the blood vessels or in the connective tissue. Complex sensory terminations were not in evidence here and I met with no intraepithelial fibres reportdely found in the epithelium of the plexus chorioideus.The sensory terminations in the pia mater, as STÖHR and others have opined