Plexus

“ The Brachial Plexus.—Lesions of the brachial plexus may be divided into those above the clavicle and those below that bone.
In the supra-clavicular injuries, the violence applied to the head or shoulder causes over-stretching of the anterior branches (primary divisions) of the cervical nerves, the fifth, or the fifth and sixth being those most liable to suffer. Sometimes the traction is exerted upon the plexus from below, as when a man in falling from a height endeavours to save himself by clutching at some projection, and the lesion then mainly affects the first dorsal nerve. ”

“ Here, still further sublimated and elaborated by the igneous power of the soul, the blood is distributed to those extremely minute vessels or capillary arteries composing the choroid plexus, which contain or are the seat of the soul itself. The arterial plexus penetrates even the most intimate part of the brain, its constituent vessels, interwoven in highly complex fashion, being distributed over the ventricles, and sent to the origins of the nerves which subserve the faculties of sensation and motion. ”

“ This seems to show that the nervous plexus, if present, has its constituent fibres aggregated into trunks in the course of the nutriment tubes.
Thus far, then, I should be inclined to adopt the nerve-plexus theory. But lastly, we come to another [24] species with a very large bell and a very small polypite. Irritation of margin or radial tubes causes the animal to go into a violent spasm, but irritation of the general muscular layer only causes an ordinary locomotor contraction. ”

“ Such a nervous plexus admits of being detected in the sub-umbrella of all Medusæ, and in some species may be traced also into the tentacles. It invariably lies between the layer of muscle-fibre and that of the epithelium. The processes of neighbouring ganglion-cells in the plexus either coalesce or dwindle in their course to small fibres: at the margin of the umbrella these 20 unite themselves with the elements of the nerve-rings. There are also described several peculiar tissue elements, such as, in the umbrella, nerve-fibres which probably stand in connection with epithelium-cells ”

“ We allude to what Western science terms the "Solar Plexus," and which it considers as merely one of a series of certain matted nets of sympathetic nerves with their ganglia found in various parts of the body. ”

“ Thus injury to a single nerve, or to a complex of two or more, was far more common than one implicating the whole plexus. Again, while complete paralysis might affect one set of nerves, another might simply exhibit signs of irritation in the form of hyperæsthesia or pain. ”

“ A plexus of fibres bringing the inner processes of such cells into communication arises, and forms something like a nervous layer capable of propagating impulses in all directions. At a subsequent stage some of the superficial cells, ceasing to be themselves the recipients of external stimuli, sink inwards and become ganglion-cells connected [304] with the nervous plexus—agents, as we must suppose, for the reception, multiplication, and diffusion of the impulses received from the outer cells. ”

“ The plexus (d′) lies close to the coats of the upper end of the stomach: several branches, proceeding from it, run further on, but I was able to trace only a few of them: one went (at least in the case of Balanus perforatus) , to the adductor scutorum muscle: another branch spread out on the flanks of the prosoma: I strongly suspect that one branch goes to the acoustic sack: it appeared, also, as if some of the small branches entered the second plexus (m) , where the inner antennular nerve and ophthalmic nerve cross over the outer antennular nerve. ”

“ These arteries supply blood by giving off branches to the muscles of the eye, sclerotic coat, iris, choroid coat, and the ciliary bodies. It gives off another branch to Harder’s gland, and finally anastomoses with the ethmoidalis.
3. The plexus temporalis, rete mirabile ophthalmicum, or wonderful network (Fig. 72, No. 8) , is formed between the second and the third trunk of the trigeminus nerve and the rete ophthalmicum.
Inferior to this is the alveolar plexus, which plexus accompanies the third branch of the trigeminus into the lower jaw. ”

“ After emerging they break up into a large anterior division and a small posterior division, the posterior branches supplying the spine and the dorsal muscles and skin, the anterior the rest of the trunk and the limbs. The cervical plexus is formed by the anterior divisions of the first four cervical nerves, the brachial plexus by the last four cervical and the first dorsal or thoracic nerves, the lumbar plexus by the four upper lumbar, and the sacral plexus by the last lumbar and the four upper sacral nerves. ”

“ The plexus pedundus is formed from the spinal nerves coming out of the plexus ischiadicus. These fibers emerge caudalward and are directed horizontally. They frequently anastomose with each other, especially on the pubic rim and on the outside of the plexus ischiadicus. These branches are deeply imbedded in the kidney substance and innervate the pubio-coccygeus, or depressor coccygis lateralis, the ilio-coccygeus, the transversalis, the sphincter, and other muscles of this region, and the skin of the anal region. ”

“ The anterior thoracic, a large nerve which springs from two or three of the posterior roots of the plexus and extends to the shoulder cavity where it branches. The anterior branch is distributed to the patagium and the front part of the pectoral muscles. The posterior branch supplies muscles along the side of the thorax and extends into the abdominal muscles. ”

“ And if the term plexus, in this application, does not represent to the Western mind the idea conveyed by the term of the Anatomist, then call them Chakras or Padmas, or the Wheels, the Lotus Heart and Petals. Remember that Physiology, imperfect as it is, shows septenary groups all over the exterior and interior of the body; the seven head orifices, the seven “organs” at the base of the brain, the seven plexuses, the pharyngeal, laryngeal, cavernous, cardiac, epigastric, prostatic, and sacral, etc. ”

“ When the whole plexus is involved, sensibility is lost over the entire forearm and hand and over the lateral surface of the arm in its distal two-thirds. All the muscles of the arm, forearm, and hand are paralysed, and, as a rule, also the pectorals and spinati, but the rhomboids and serratus anterior escape. There is paralysis of the sympathetic fibres to the eye and orbit, with narrowing of the palpebral fissure, recession of the globe, and the pupil is slow to dilate when shaded from the light. ”

“ Another very important reflex upon the heart is that which is effected through the solar plexus and the sympathetic nerve. A stroke upon the belly will through these nerves stop the heart, dilate the vessels, and induce the most serious conditions of shock, killing the patient, or at any rate bringing him down to death's door. ”

“ Nervous System.—The nervous system is present in all divisions of the order. It consists of a paired, anterior ganglion lying ventral to the gut, and from this are given off, right and left, dorsal, lateral and ventral fibres interconnected by a plexus. The nerve-cells are scattered throughout the plexus. The chief development of the system occurs in relation to the muscular body-wall, sense-organs and the pharynx. ”

“ Close behind the stomach is a group of ganglia, the solar plexus, which sends out a large number of nerve-filaments that communicate with the brain, and thus suggest the physiological explanation of the curious phenomenon, though its final or teleological purpose is somewhat less apparent. ”

“ This nerve is frequently small or absent in the Platana.
[In the Frog, the seventh, eighth, and ninth nerves unite to form the sciatic plexus which gives rise to the large sciatic nerve extending along the thigh, and dividing above the knee into the tibial and peroneal nerves to the leg and the foot. The tenth nerve is present.]
2. The Sympathetic Nervous System.
This system consists of a cord on each side closely following the course of the systemic arches and the dorsal aorta. It has on it six ganglionic swellings, and there are connections between the ganglia and all the spinal nerves. ”

“ Brachial plexus.—Entry, 2 inches above the clavicle at the anterior margin of the trapezius; exit, first intercostal space, 1 inch from the sternal margin. Heavy dull pain developed at once, extending down the upper extremity. A fortnight later this pain still persisted; there was lowered sensation in the ulnar area with formication, also lowered sensation in the internal cutaneous area of distribution; sensation in the lesser internal cutaneous area was normal. The patient went home with the nerve symptoms well at the end of a month.
(119) Brachial plexus injury.—Wounded at Magersfontein. ”

“ In another group of diseases of the genital organs, the disturbances of cardiac activity may be brought about by pressure which, in consequence of the morbid processes in the reproductive organs, is exercised upon individual nerves or upon an entire nerve plexus. ”

“ However the nerves of organic life always predominate in these plexuses. There is only the pulmonary in which the par vagum particularly predominates, whilst the nerves coming from the inferior cervical ganglion are, if we may so say, but accessory. ”

“ The nerves also undergo division until they terminate as fine thread-like structures in all parts of the body. The distribution of nerve terminations, however, is not uniform, as might be supposed, but the skin and important organs like the heart, stomach, and muscles are the more abundantly supplied. On many of the nerves are small rounded masses, called ganglia, and from many of these small nerves also emerge. At certain places the nerves and ganglia are so numerous as to form a kind of network, known as a plexus. ”

“ The peripheral system is somewhat complex and numerous intercommunications are established by which nerve impulses originating in the central axis and leaving by one part of the peripheral system may exercise a controlling influence over another part. Plexuses, or intertwinings of nerve axons, are so numerous and complicated that it is difficult to follow each set of nerve stimuli from their origin to their final destination and effect without considerable study. ”

“ The primitive plexuses resulting from the interlacing of the organic nerves at their exit from the ganglions, form a mass of irregular nerves, buried in the cellular texture, accommodated to the forms of the neighbouring organs, and wholly different from those of animal life, as of the brachial, the lumbar, &c. ”

“ The ganglia and the plexuses stand in mutual opposition, like the branchiæ and intestine, like artery and vein, like blood and lymphatic vessels. The ganglia oxydize, polarize; they are the active. The plexuses suffer, digest, and are the recipient.
2031. The visceral nerves, like the viscera, act for themselves, being unconcerned for the animal systems.
2032. The visceral nerves have a vegetable sensation360 for themselves, a sense of touch, such as the blossom might have in the instant of the pollenization. ”

“ I confess, that I know not how to class these organs. We cannot deny that they have the greatest analogy in structure to the others. They are approximated in another respect, which is this, that the nerves, in going from them, form265 almost immediately plexuses that we have designated under the names of cervical, brachial, lumbar, and sacral, in the same way as the solar, cardiac, mesenteric plexuses, &c. are formed by the nerves of organic life, at the moment they go from their respective ganglions. However, these last nerves are conductors of very different properties. ”

“ If any one who may not just like an actual dissection, will look at one of Quain's 'Plates of the Bones, Muscles, and Nerves of the Human Body,' he will see that, growing as it were out of the walls of the stomach, there are, in our wonderful human machine, great bunches of nerves, called, by the medicals, the 'great ganglionic system,' and he will observe that these nerves are in intimate and inseparable connection with the spinal cord, and the brain. ”

“ The cells of the spinal cord also send out branches to the body and to other cells in the brain.
10. How we Feel.—If we cut or burn ourselves we suffer pain. Can you tell why it hurts us to prick the flesh with a pin, or to pinch or burn or bruise it? It is because the flesh contains a great many nerve-branches from the brain. When we hurt the skin or the flesh, in any way, these nerves are injured. There are so many of these little nerves in the flesh and skin that we cannot put the finest needle into the flesh without hurting some of them. ”

“ In man, standing erect, the heart is situated above its chief reservoir—the abdominal veins. The blood is raised by the action of the respiratory movements, which act both as a suction and as a force pump, for the blood is not only aspirated into the right ventricle by the expansion of the thoracic cavity, but is expressed from the abdomen by the descent of the diaphragm. When a man faints from fear, his muscular system is relaxed and respiration inhibited. The blood in consequence sinks into the abdomen, the face blanches and the heart fails to fill. ”

“ Immediately a dull, sickening pain becomes apparent at the base of the neck, and insensibility rapidly ensues. This arises from the affection of the respiratory nerve centre. In a short space of time the face becomes dark and congested through the veins being gorged with blood, and the heart ultimately ceases to beat. ”