Observations on certain parts of the animal oeconomy. Inclusive of several papers from the Philosophical transactions, etc / by John Hunter ... With notes by Richard Owen.
- John Hunter
- Date:
- 1840
Licence: Public Domain Mark
Credit: Observations on certain parts of the animal oeconomy. Inclusive of several papers from the Philosophical transactions, etc / by John Hunter ... With notes by Richard Owen. Source: Wellcome Collection.
421/494 page 413
![The organ is supplied with nerves from the medulla spinalis, from which they come out in pairs between all the vertebrae of the spine. In their passage from the spine they give nerves to the muscles of the back, &c. . They bend forwards and outwards upon the spine, between it and the muscles, and send out small nerves to the ex- ternal surface, which join the skin near to the lateral lines. These ramify upon the skin, but are principally bent forwards between it and the organ, into which they send small branches as they pass along. They seem to be lost in these two parts. The trunks get upon the air-bladder, or rather dip between it and the muscles of the back, and continuing their course forwards upon that bag, they dip in between it and the organ, where they divide into smaller branches; then they get upon the middle partition, on which they continue to divide into still smaller branches; after which they pass the length of the body; and in the trunk the two nerves exceed the size of the spinal chord. In osseous fishes it is relatively smaller, and in some species, as the cod, is formed by a combination of a branch of the fifth with a filament of the eighth or nervus vagus, Besides the class of fishes (with the exception of the myxine), the lateral nerve is also present in those reptiles which preserve thronghout life the external branchie or the branchial apertures, and whieh reside habitually in water, and move, like fish, by the actions of a caudal fin. In the Menobranchus the nervus lateralis forms a large branch of the nervus vagus, and passes superficially be- neath the skin as far back as the middle of the tail, where it joins the filaments of the spinal nerves. In the proteus the nervus vagus sends off on each side two nervi laterales, one deep-seated, the other superficial. In the mencopome the lateral nerve is likewise present, but is much more delicate than in the Perennibranchiata with external gills, In the larva of the Rana paradowa the lateral nerve may be observed beneath the skin in the longitudinal fissure which Separates the two large muscular fasciculi of the tail on each side. After the full formation of the anterior extremities this nerve becomes gradually more attenuated, and finally disappears with the absorption of the tail. It does not exist in the anourous batrachia. We may thus perceive a relationship of co- existence to subsist between these enigmatical nerves and branchial respiration. This imperfect kind of respiration is assisted by the vascularity and active powers of excreting mucus in the whole or a part of the external tegument. In the osseous fishes a linear series of mucous follicles is extended along each side of the body, and the lateral nerves, which run parallel with these lines give numerous branches to the mucous sacs and the neighbouring skin; and in the Perennibranchiata the lateral nerves are exclusively distributed to the skin: hence they might be termed the cutaneous respiratory nerves. They do not sup- ply the muscles along which they pass; these derive their nervous energy from the ordinary spinal nerves. When irritated or galvanized the lateral nerves excite no contractions in the muscles; they are therefore not analogous to the Spinal accessory nervesin the mammalia. In the Gymnotus Mr. Hunter was not able to trace any nerves going from the lateral nerve to join those from the me- dulla spinalis which supply the electric organ, but it anastomoses with the spinal nerves which supply the caudal fin. And in the cod, where this anastomosis takes place at each of the numerous fins, Mr. Swan conjectures that its function may be to produce sympathy and harmonious coéperation, and to regulate and produce, independently of the will, the action of the muscles of these parts. (See his accurate and beautiful Illustrations of the Comparative Anatomy of the Nervous System, p. 26, pl. vii.) And this theory equally agrees with the laws of coexistence of the lateral nerves as established by an extensive induction of particular dissections. ] 36%](https://iiif.wellcomecollection.org/image/b33292292_0421.jp2/full/800%2C/0/default.jpg)
