1 with the addition of NF, neural fossa protecting the aggregated ganglia of the central nervous system; PVP, left posterior ventral process; PMP, posterior median process.
Bourne (5) to of NC, neural canal or foramen.
Snp, Sub-neural arch.
These are a ventral arch forming a neural canal through which the great nerve cords pass (figs.
The figure B also shows the peculiar neural investiture formed by the cerebral arteries in Limulus and the derivation from this of the arteries to the limbs, III, IV, VI, whereas in Scorpio the latter have a separate origin from the anterior aorta.
Fins without spines; caudal fin, if present, without expanded hypural, perfectly symmetrical, and supported by the neural and haemal spines of the posterior vertebrae, and by basal bones similar to those supporting the dorsal and anal rays.
The simple nerve-ganglion or brain (g) lies on the anterodorsal side of the pharynx, and by its position determines the orientation of the animal, the cloacal opening lying on the same side, and the course of the gut being" neural."The sense organs are a pair of pigmented eyes (oc), and two pairs of antennae, one anterior proximal and near the wreath, the other distal and usually more or less lateral.
In the female the same growth of epithelial cords into the mesenchyme of the genital ridge takes place, but each one is Neural tube.
Gastrocnemius, tonic contraction obtains; but this, like the last mentioned, is not autochthonous in the muscles themselves; it is indirect and neural, and appears to be maintained reflexly.
The work of Camillo Golgi (Pavia, 1885 and onwards) on the minute structure of the nervous system has led to great alteration of doctrine in neural physi nerve cells, that is to say, the fine nerve fibres - since all nerve fibres are nerve cell branches, and all nerve cell branches are nerve fibres - which form a close felt-work in the nervous centres, there combined into a network actually continuous throughout.
A prominent and practically important illustration of neural tonus is given by the skeletal muscles.
It is with the neural element of muscle tonus that tendon phenomena are intimately associated.
The jerk is obtainable only from muscle fibres possessed of neural tonus.
The areas of intervening cortex, arriving at structural completion later than the above sense-spheres, are called by some association-spheres, to indicate the view that they contain the neural mechanisms of reactions (some have said "ideas") associated with the sense perceptions elaborated in the several sensese spheres.
- anp, Anterior neural pore; be, rudiment of buccal skeleton; c, cilia; cb, ciliated band; cc, ciliated groove; cm, cilia at margin of mouth; gl, external opening of club-shaped gland; Hn, Hatschek's nephridium; lm, left metapleur; n, notochord; pp, praeoral pit; ps, primary gill-slits, I, 5, and 13; rm, right metapleur showing through.
The primordium of the neurochord (neural or medullary plate) referred to above becomes closed in from the surface by the overgrowth of surrounding epiblast, and its edges also bend up, meet, and finally fuse to form a tube, the medullary or neural tube.
An important fact to note is that the blastopore is included in this overgrowth of epiblast, so that the neural tube remains for some time in open communication with the archenteron by means of a posterior neurenteric canal.
It is still longer before the neural tube completes its closure in front, exhibiting a small orifice at the surface, the anterior neuropore.
(Adapted from Hatschek.) pc, Praechordal head-cavity of embryo; cc, collar-cavity (first somite); my, mesodermic somites (myocoelomic or archenteric pouches); ch, notochord with the neural tube (neurochord) lying upon it; np, anterior neuropore; ne, position of posterior neurenteric canal.
The vertebral axis shows a series of broad rings, with distinct neural arches, but no ribs.
Towards the end of the body both neural and haemal arches are continued into forked radial cartilages, which support a median fin.