Comparative anatomy / by C.Th. v. Siebold and H. Stannius ; translated from the German, and edited with notes and additions recording the recent progress of the science by Waldo I. Burnett.

  • Karl Theodor Ernst von Siebold
Date:
1854
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Licence: Public Domain Mark

Credit: Comparative anatomy / by C.Th. v. Siebold and H. Stannius ; translated from the German, and edited with notes and additions recording the recent progress of the science by Waldo I. Burnett. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    laterally, thus forming a ring (the oesophageal ring) through which the oesophagus passes. §147. The histological elements of the nervous system of these animals, are arranged in the following manner: (1) o o The central mass of the nervous system is enveloped by a fibrous tissue (Neurilemma), of longitudinal and transverse fibres which are often covered with special pigment cells. The nervous cords and filaments are composed of extremely fine, primi- tive fibres, between which in the ganglia are situated various-sized cell-like ganglionic globules.® Some of these primitive fibres pass from the cere- bral ganglion through all the ventral ganglia, while others pass off from the central ganglia to the peripheric nerves. Many of the ganglionic globules of the brain and abdominal cord are remarkable for their longer or shorter prolongations which may be traced even into the roots of the nerves.® § 148. The nerves are given off usually from the ganglia, and rarely from the interganglionic cord. The cerebral ganglion sends off nerves to the organs of sense in the head, and to the labial, proboscideal, and masticatory organs about the mouth. Its development therefore corresponds exactly to the more or less complicated condition of the cephalic extremity. The ventral ganglia send off from each side usually two or three sym- metrically-arranged main nerves to the muscles and skin. It is with the Annelides that there have been found the first traces of a vegetative or splanchnic nerve (Nervus splanchnicus). This consists of deli- cate filaments which are distributed upon the intestinal canal, with here and there enlargements, and which anastomose, some directly with the oesophageal 1 Our knowledge of the intimate structure of the nervous system of the Annelides is as yet based upon researches of that of the Hirudinei only *, see Helmholtz, De fabrica systematis nervosi everte- bratorum dissertatio. Berol. 1842, p. 12 •, Hanno- ver, Recherches microscopiques sur le systthne nerveux, Copenhague, 1844, p. 72-, Will, Vorlau- fige Mittheilung fiber die Struktur der Ganglien und den Ursprung der Nerven bei wirbellosen Thieren, in Muller's Arch. 1844, p. 82 •, Ehren- berg, Beobachtung einer auffallenden, bisher uner- kannten Struktur des Seelenorgans bei Menschen und Thieren, in the Abhandl. d. Berl. Akad. 1834, p. 720, Tab. VI. fig. 7 *, and Valentin, Ueber den Verlauf und die letzten Enden der Nerven, in the Nov. Act. Acad. XVIII. 1836, p. 202, Tab. VIII. 2 Valentin declares that he has seen in the brain * [ § 147, note 3.] This alleged relation of the elements of the nervous tissue is a point of no little histological importance and I shall give it a special consideration in noticing the minute structure of this tissue with the higher animals. I have made no observations on the animals in question, but 14 and ventral ganglia of the leech so regular and symmetrical an arrangement of the ganglionic globules, that those of the two lateral halves cor- responded exactly as to number, volume and posi- tion 5 see Valentin, loc. cit. p. 208, Tab. VIII. fig. 62, &c. This symmetry must appear highly aston- ishing. 3 These prolongations give the ganglionic glob- ules a clavate aspect, as already seen and figured by Ehrenberg (loc. cit. Tab. VI. fig. 7, and fig. 7.ll., 7.12 ). Further researches must decide if these prolon- gations are really continuous with the primitive nervous fibres, as Helmholtz (loc. cit. p. 15), and Hannover (loc. cit. p. 73, Tab. VI. fig. 78), affirm to be the case ; for, Valentin in his apparently so careful researches, has never Seen any trace of a clavated or pedunculated ganglionic globule.* Ley dig, an excellent observer, confirms the gen- eral view here advanced of the direct connection of the ganglionic globule with the nerve-tube ; see loc. cit. p. 130, Taf. X. fig. 67 (Piscico/a). See also Bruch, Siebold and Kb Hiker's Zeitsch. 1849, p. 175, Taf. XII. fig. 7, 8, 9. — Ed.