The meninges in lower vertebrates are very different from those in mammals and man.
Though formerly—misled by superficial resemblances—a dura mater, arachnoidea and pia were supposed to exist also in cyclostomes and plagiostomes, at the present time this supposition is maintained only in the "Mikroskopische Anatomie der Wirbeltiere (Heft IV)", published in 1923, by R. Krause, who, however, does not seem to have studied this subject accurately.
In 1884 Sagemehl pointed out that a real arachnoidea does not occur in fishes, and that the wide meshed tissue formerly considered as such really lies between the so-called internal and external (periosteal) dural membrane, and in his study on the comparative anatomy of the meninges, Sterzi1 emphasized that in cyclostomes and plagiostomes only one undifferentiated meninx is found, which he called meninx primitiva, and considered to be the origin of the dura, arachnoid and pia in higher animals.
It should, however
KAPPERS CUA. THE MENINGES IN LOWER VERTEBRATES COMPARED WITH THOSE IN MAMMALS. Arch NeurPsych. 1926;15(3):281–296. doi:10.1001/archneurpsyc.1926.02200210002001
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