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tility in the walls of the alimentary canal greater than resides in the sareode substance, a scries of fibres are produced within the BarcodeThese fibres arise neither from cells nor from endoplastfl. At first it ■would seem that lines of the sarcode itself assume a parallel direction and a contractile function, but at length a difference in structure may be detected between the fibres and the rest of the layer, and it becomos evident that a special contractile apparatus has been constructed. That the sarcode, which in its perfectly structureless condition was capable of manifesting all the essential functions of organic life, was through its own inherent vital activity the sole agent in producing these changes, I can scarcely doubt. No nervous system is developed in the pseudembryo, and the combination and harmony of action of the various organs and parts of the organism is maintained by a property which resides in the structureless sarcode equivalent to the action of the nervous system.
A portion of the general sarcode substance now becomes somewhat more dense by an accumulation of oil-cells and granules, and is at length moulded into a disk which rapidly develops the apical pole of the Urchin with its rudimentary ambulacral vessels. Bound this, and involving the stomach of the pseudembryo, the permanent organs are gradually built up. The simplest mode of expressing the essential nature of this process may possibly be, that the sarcode, previously apparently homogenous, separates by a form of fission or internal gemmation into two portions, of which one develops and maintains a set of temporary organs whose function is evidently to provide for the nutrition of the embryo and for the diffusion of the species, while the other portion produces the true embryo. But, if I am correct in my view with regard to the plan of the development of the pseudembryo, if I am right in believing that the life of the zooid resides in the sarcode, and in the sarcode alone; that the sarcode performs, as in the Protozoa, all the essential functions of life, and that the tissues and organs are mere inert accessory apparatus, active and living only through the influence of the sarcode which permeates and which has produced them, it would surely be unphilosophical to attribute the formation of the group of organs produced by the bud to a process essentially different, or to deny to the sarcode forming and permeating the tissues and organs of the young Urchin, the same paramount placo in its economy, which I am forced to accord it in the Pseudembryonic Zooid.
LXXIII.—Oir Some Variations In The Arrangement Of The Nerves Of The Hitman Body. By ¥m. Turner, M.B. (LoncL), F.B.S.E., Senior Demonstrator of Anatomy in the University of Edinburgh.
The following examples of deviations from the usually described arrangements of the nerves, taken from my Dissecting Boom NoteBook, may perhaps prove of interest to those engaged in the study of variations in human structure.
Branches of the Fifth Cranial Nerve.—On the left side of an adult, the buccal nerve arose from the inferior dental nerve in the dental canal. It then entered a small canal, which opened externally by a small foramen in the alveolar border of the lower jaw, close to the ascending ramus. It then passed through the buccinator muscle in the usual way. On the right side the distribution was normal.
On the left side of another subject the mylo-hyoid branch of the inferior dental nerve gave off a branch of comparatively largo size, which pierced the mylo-hyoid muscle, and joined the gustatory nerve of the same side.
Branches of the Nervus Vagus.—In another subject the lower cervical cardiac branch of the right pnoumogastric, instead of passing to the deep cardiac plexus, crossed in front of the transverse part of the arch of the aorta, and joined the superficial plexus. On the other hand, the cardiac nerves of the left side passed behind the arch to the deep plexus.
On two, if not three occasions, I have seen the descendens noni nerve arise from the trunk of the pneumogastric high up in the neck (ride Quain and Sharpey). This irregularity in the place of origin may not perhaps seem so remarkable, if we bear in mind that the hypoglossal and vagus nerves are intimately connected together just beneath the basis cranii. In these eases it is probable that the descendens noni fibros of the hypoglossal are given off in the first instance to the vagus; that they accompany that nerve for a short distance, and then leave it apparently as one of its branches.*
In three cases in which the right subclavian artery arose, as a separate branch from the left side of the aorta, the inferior laryngeal branch of the right vagus, iustoad of turning round the right subcla
* Sec also a note to the English Translation of Cruvcilhier's Anatomy, p. 1141.
vian, passed almost directly inwards to the larynx. This arrangement has also been described by other anatomists in similar cases of irregularity of the right subclavian. In another case, where the aorta arched to the right side, the right recurrent nerve hooked round it, whilst the left recurrent turned round the end of the ductus arterioru8. I have offered an explanation of the mode of production of these irregularities of the recurrent nerves in my memoir on the irregularities of tho aorta and its primary branches.*
The Spinal Accessory Nerve.—This nerve, in its passage downwards, generally crosses in front of the internal jugular vein, but I have now, in a considerable number of cases, seen it pass behind that vessel. In two cases, I observed it go behind the sterno-mastoid muscle, instead of perforating it.
Nerves of the Cervical Plexus.—The nervus occipitalis minor varies much in size in different subjects, and apparently bears an inverse relation to the size of the great occipital. Sometimes, instead of ascending parallel to the posterior margin of the sterno-mastoid, it inclines obliquely backwards away from that muscle, when it either may or may not pierce the trapezius in its course to the scalp, according to the extent of attachment of that muscle to the superior curved line of the occiput. "When this arrangement occurs, one sometimes sees a small nerve passing upwards to the scalp behind the ear, lying on the sterno-mastoid muscle, a short distance from its posterior margin. Cruveilhier states in his Descriptive Anatomy, that the small occipital nerve does not send branches to the auricle; but I can, from more than one dissection, confirm the statement made by Professor Ellis, that it gives a branch to the upper part of the cranial aspect of the auricle. The ascending branch of the superficial division of the cervical plexus, which lies parallel to the external jugular vein, I have frequently seen. On one occasion I saw the posterior belly of the omo-hyoid muscle receive its nerve of supply direct from the communicans noni of the cervical plexus, and not from the descendens noni of the hypoglossal.
Nerves of the Brachial Plexus.—The large nerves which form the brachial plexus usually lie in the upper part of their course behind the anterior scalene muscle; but it is not unfrequent to find the fifth cervical nerve, and less often the sixth cervical also, piercing the upper fibres of that muscle. Still more rarely the fifth cervical
* British and Foreign Medico-Chimrgical Review, July and October, 1862.
nerve is situated completely in front of the scalenus anticus. There are many variations in the mode of junction of these lower cervical nerves with each other, where they form the plexus. Thus the seventh cervical nerve may join the cord formed by the fifth and Bisth, which is perhaps the most usual arrangement; or it may divide and give a large branch to that cord and a small one to the lower cord, or vice versa. The place of junction of these divisions with the upper and lower cords also varies, sometimes it is near the scaleni, at others further outwards. Then the extent to which the upper and lower cords contribute in the axilla to the formation of the third or posterior cord is very (Liferent; at times the upper gives a very large branch, the lower a comparatively small; or the lower a large and the upper a small; or perhaps these branches may bo almost equal in size. The branch which the fifth cervical contributes to the phrenic may, instead of joining that nerve almost immediately, run down independently on the surface of the scalenus anticus, and not blend with the phrenic till just above the first rib.
In one ease I saw the right anterior thoracic branch of the outer cord of the plexus give off branches to the clavicular fibres of the deltoid muscle, and in the same body the external respiratory nerve of Bell arose from the fifth, sixth, and seventh cervical nerves. The musculo-cutancous branch of the outer cord of the plexus not unfrequently exhibits variations in its arrangement. Thus, instead of piercing the coraco-brachialis muscle, it may run in the same fasciculus with the median for some distance down the upper arm, and then leave it in two or more divisions, branches from some of which enter the muscles of the front of the upper arm, whilst the remainder join to form the external cutaneous nerve of the fore arm. Or again, it may pierce the coraco-brachialis muscle, and then give oft" a branch (in one example I dissected this was of some size), which joins the median lower down in the upper arm.
The inner and outer heads of the median nerve present many variations, not only as regards their relative side, but their mode of origin. Either, or both may, instead of presenting a single cord, be double. If the inner, then the brachial artery is crossed by two cords instead of one, and theso may either vary, or be of almost the same size. In one very remarkable case, the outer head of the left median nerve arose about the middle of the upper arm from the musculocutaneous, and passed almost immediately behind the brachial artery to join the inner head, which had accompanied the artery on its inner side so far down the limb. In this case the brachial artery had not a head of the median nerve crossing in front of it. I have now seen the trunk of the median nerve several times pass behind the brachial artery, instead of in front of it, on a line with tho tendon of insertion of the coraco-brachialis muscle. In three of those interesting irregularities which I have recently examined, where, correlatively with the development of a process from the side of tho humerus above its inner condyle, the brachial artery was displaced and passed behind that process, the median nerve trunk closely accompanied the artery, and was situated on its inner side.* In the right arm of a male I saw the circumflex nerve, in addition to its normal muscular branches, give off a long and slender nerve to the teres major.
In one case I saw the right ulnar nerve in tho fore arm not only supply, as usual, branches to the flexor carpi ulnaris, and inner part of tho flexor profundus digitorum, but also two branches to the flexor sublimis digitorum.
The distribution of the digital nerves to the sides of tho fingers also present occasional variations, which chiefly consist in an increase in the number of fingers usually supplied by one trunk, say the ulnar, and a consequent diminution in tho number of fingers supplied by the median or radial, according as the ulnar increase is on the palmar or dorsal aspect.
The Inlercosto-Humeral Nerves.—On several occasions I have seen the first intercosto-humeral nerve to be derived, as a lateral cutaneous branch, from the first dorsal or intercostal nerve; in which cases it communicated with the nerve of Wrisborg in the axilla. When traced upwards to its origin, it passed along the inner surface of the first rib, then upwards next the oiitcr surface of the pleura as far as the trunk of the first dorsal nerve, where it was lying in front of the neck of tho first rib. An intercosto-humeral branch from the second intercostal nerve, but none from the third, was present in these cases.
Nerves of the Lumbar Plexus.—In ono instance the obturator nerve aroso chiefly from the second and third lumbar nerves, the branch passing to it from the fourth lumbar being but small. In this case the greater part of the fourth lumbar passed down as a large cord to join the fifth, in order to form the lumbo-sacral cord. I have very seldom seen the accessory obturator nerve: the proportion in
• By far the best and most exhaustive account of tho anatomy of the supracondyloid process is to be found in the Monograph by Wenzel Gruber, in the Mem. de l'Acad. Imp. dc St. Petersburgh, vol. 8, 1859.