as some modern writers have erroneously supposed, but at their roots, where they grow, as it were, from the bifurcated trunk of the trachea, which, where it again divides, becomes in a measure fixed by its attachment to the great bloodvessels and the spine. So also shall we find the enlargement of the chest to be peripheral nearly in all directions, the spine being the fixed centre. Its chief increase is indeed downwards and around its lower portions; but if we watch the upper parts with relation to the spine, we can plainly see them also rise and expand considerably. This general enlargement of the chest may be analysed into its enlargement downwards, upwards, and outwards. The enlargement of the chest downwards is, as you know, effected by the action of the diaphragm, which in its passive state projects in a very convex form upwards into the chest, but when acting, its muscular margins and pillars draw its tendinous centre downwards towards their attachments to the lower margins of the ribs and sternum, and the upper lumbar vertebræ. In the same contraction the muscular portions of the diaphragm being straightened towards the centre, touch the ribs at fewer points, and form angular spaces, in which the thin marginal lobes of the lungs become expanded downwards. Now as this downward action of the diaphragm cannot take place without pressing on the contents of the abdomen, it causes an outward movement of these contents, and the swelling of the abdomen at each inspiration therefore becomes an index of this action. The enlargement of the chest upwards, by which the apices of the lungs are expanded, is effected by the drawing upwards of the upper ribs, sternum, clavicles, and scapula, by the sterno-mastoid, scaleni, and other muscles, which connect this upper frame work of the chest direetly or indirectly with the upper end of the spinal column. This motion, although not great in ordinary respiration, is yet in proportion to the extent of the upper lobes of the lungs. It has been overlooked by many physiologists, but it is highly important as a source of diagnosis; and you may perceive and measure it if you keep steady the spinal column by stand. ing with the back against a pole, or the edge of a door, or the corner of a wall; you will then see that the upper ribs rise to the amount of half an inch or more in cach inspiration; and so far from being, as Haller and others maintained, almost fixed, they are, in proportion to their length, actually more moveable than the lower ribs. If you examine their attach. ments to the vertebræ, you will there perceive that the upper ribs admit of more you motion than the lower. Magendie, I believe, first pointed out this important part of the movements of respiration, and now see how it accords with the expansion of the lung which I have just exhibited to you. The outward enlargement of the chest is mainly effected by the contraction of the intercostal muscles. I dare say that you may have heard or read of the long discussions which were formerly excited by this apparent paradox, that of a cavity being enlarged by the contraction of its walls. It is, indeed, a mechanical process hard to be described, and yet how plain and simple it is on inspection! See how these ribs, especially the lower, in their collapsed state, are convex downwards in the portions anterior to their centres. Well, now, these are their most moveable portions, and if they are drawn upwards, the ends being comparatively fixed, you see that their downward convexity is diminished, and their outward convexity or inward concavity is enlarged, and thus the horizontal diameter of the chest is increased. But observe, for this effect it is necessary that the ribs should be drawn upwards; and what is it that makes the contraction of the intercostal muscles draw the ribs upwards rather than downwards? Haller and others say it is because the upper ribs are fixed, and cannot be drawn downwards; but we have just seen that they are not fixed: the fact is that they are drawn upwards themselves by muscu lar action, and this upward traction is communicated and increased to the ribs below by the contraction of their respective intercostal muscles. If instead of drawing up, or fixing the upper ribs, you draw down, or fix the lower ones by the abdominal muscles, then the intercostal muscles become means of diminishing the diameter of the chest by drawing the ribs downwards; and they actually do contribute to this end in forcible acts of expiration. Now here is a case illustrating the necessity of learning the mechanism of the chest rationally, and not merely by rote. You see that both sets of intercostal muscles, external and internal, must tend to elevate the ribs as long as the upper ribs are either fixed or drawn upwards; but when the lower ones are fixed, the contraction of the intercostals must approach them to this lower fixed point. Well, now, let us go back a moment, and apply the same question to the diaphragm, whose ordinary action we found to be to enlarge the chest downwards by the drawing down of its central convexity. This supposes its tendinous centre to be the most moveable attachment of the muscular portion of the diaphragm, that to the lower margin of the ribs and sternum being more fixed. But the centre of the diaphragm is sometimes more or less fixed, and prevented from descending, by tumors or excessive tenderness of some of the abdominal viscera below it. How will its muscular margin then act? Why, it will draw upwards its lower attachment with the ribs and sternum, and thus increase the capacity of the chest by raising it from the fixed convexity of the diaphragm. When, therefore, you see a patient breath. ing merely by the heaving of his chest, you are not to suppose that the diaphragm is inactive, for it may thus contribute to inspiration that is wholly thoracic. This upward action of the diaphragm in not considerable in common cases; but it must always be something-that something being the amount of resistance offered to the descent of the diaphragm by the contents and walls of the abdomen." There is another particular in the ordinary action of the diaphragm which is worthy of your notice, because it may prove a source of physical signs. You see, by these diagrams, that considerable parts of the upper abdominal viscera, the liver, the stomach, and the spleen, although below the diaphragm, yet are contained within the walls of the chest. Now the portions of these walls which contain them differ from those above the diaphragm, in being subjected to the everrepeated outward pressure of these viscera, pushed by the descending diaphragm; and the result of this pressure is a permanent bulging or prominence in the lower part of the chest, and a slight furrow or depression above it. This depression generally marks the situation where the lung begins, and where the abdominal viscera cease to be in contact with the walls, although they generally rise above it towards the centre of the chest. The existence of this furrow, and its use as a sign of limits, were first pointed out to me by my friend Dr. Edwin Harrison, and I think I may explain its production by the outward pressure of the sub-diaphragmatic viscera. The position of this furrow varies in different subjects, but may generally be traced from the lower end of the ster. num running horizontally around the chest, about, but not parallel with, the seventh and eighth ribs at the sides. The effect of the reiterated outward pressure of the subdiaphragmatic viscera is remarkably seen in the eversion of the lower ribs and sternum in ricketty children, the bones and cartilages being permanently bent by it. If the belly in these cases be also tumid, the upward action of the diaphragm will draw the sternum forwards and upwards, forming what is called a chicken-breast. We need not dwell long on the ordinary means by which the capacity of the chest is diminished. When the diaphragm ceases to contract, the weight of the viscera and walls of the abdomen force back the diaphragm to its wonted vaulted projection into the thorax: the same weight to the lower ribs, together with the elastic torsion of their cartilages and ligaments, make the ribs collapse on the relaxation of the intercostals and the muscles which raise the upper part of the chest. The merely mechanical constitution of the chest is in favour of its diminution, and so is that of the lungs, which we shall notice by and by; but expiration may be most powerfully assisted and increased by a great many muscles, especially the abdominal muscles, and all those connecting any of the ribs with a part of the spine below the attachments of these ribs. So, likewise, forcible inspirations are assisted by the action of all those muscles connecting any of the ribs with any part of the spine above the attachments of these ribs. A BRIEF ACCOUNT OF IRREGULARITIES IN THE HUMAN ARTERIAL SYSTEM, OBSERVED DURING THE SESSION OF 1836-37. To the Editor of the Medical Gazette. SIR, You will oblige me by inserting the accompanying paper in your widely circulated journal. Your obedient servant, HAMILTON LABATT, Demonstrator of Anatomy, Royal Coll. of Surgeons, Ireland. Dublin, Sept. 7, 1837. On taking a view of the different accounts which have been given of the varieties in the arteries of the human body, it is somewhat remarkable to observe the very few instances in which the state of the arterial system on both sides of the body has been specified. If, for instance, we examine the splendid work by Tiedemann on this subject, we find 19 cases of irregularities in the 14 of which were on the right side, and arteries of the upper extremity delineated, but 5 on the left; no mention, with the exception of two or three examples, is made of the opposite extremities. Now, inasmuch as the arterial distribu tion of one side is by no means an index of that of the opposite one, so we must immediately see how desirable it would have been that the state of both had been more frequently alluded to. Thus we should have been enabled to draw some average calculations which might prove useful in a practical as well as a physiological point of view. Arterial irregularities are generally symmetrical, but we may have the arteries of one side perfectly normal, while the corresponding vessels of the opposite side are abnormal; or lastly, irregular distributions may exist on both sides, yet totally different from each other. A remarkable instance of the last occurred to me during the season, and I procured a drawing of it, in consequence of a peculiar disposition of the thyroid arteries, which, as far as I know, has been hitherto unnoticed. On the left side I could not discover a vestige of those vessels; on the right, the superior came off from the carotid at its bifurcation, and the inferior from the first stage of the subclavian; no thyroid axis existing. Next with respect to the mammary arteries, the right proceeded from the subclavian in its third stage, and passing inwards, under the interior scalenus, sought its usual destination. The left mammary arose from the second stage of the subclavian. Lastly, in the same case, the left vertebral passed from the arch of the aorta between the left subclavian and carotid. This irregularity of the left vertebral is by no means uncommon in the human subject. According to Tiedemann it is normal in the Phoca vitulina. Before I pass on to another division I may mention a second remarkable deviation in the thyroids. It was an instance of the inferior thyroid being deficient on the left side, and the superior on the right. Meckel and Green have recorded examples where there was no inferior thyroid, but I do not find any of their cases corresponding with the above. With the exception of the case already mentioned, of the vertebral proceeding from the arch of the aorta, I have bad an opportunity of noticing but two other instances of irregularities in the vessels proceeding from that great trunk. In both, the left carotid arose from the innominata, and passing across the trachea ascended, as usual, on the left side of that tube. In one of them, the artery was given off immediately at the origin of the parent trunk, and the unusual size of the vessels in this case particularly attracted. me. The diameter of the aorta, found by taking of the circumference, exceeded 14 inch, and the innominata nearly equalled a regular aorta. The subject was an adult male, and the vascular system throughout the body was developed in an equally remarkable degree. The preparation is preserved in the College Museum, and the drawing in my possession represents the above measurements. A similar example occurred here in the course of last season, and was brought before the Chirurgical Society by Mr. Williams, who presented the preparation to the School Museum. In his case, however, the left carotid was more connected with the front of the trachea above the sternum, so as to interfere with the line of incision practised in tracheotomy. In neither of my cases was it so disposed, being, in both, completely substernal in the whole of its transverse course, and not liable to interfere with the success of such an operation as long as the mesial line above the sternum was observed. In one of them the left vena innominata might have been endangered, as it was situated higher than usual. If we consider the above irregularity in another point of view, it will be interesting to remark that it represents the normal type in some animals, as the marmot, guinea-pig, &c. Connected with the axillary artery, I met with an example nearly similar to one given by Tiedemann, of an irregular branch, in size equalling the ulnar, (analogous in many respects to the profunda femoris,) proceeding from that trunk at the lower border of the lesser pectoral, and, after giving off the subscapular and circumflex, passing between the roots of the median nerve, and running down the arm internal to the main trunk, to terminate in the anastomotic, after having given off the profunda. In this subject, the brachial plexus was quite posterior to the axillary artery. High bifurcation of the brachial artery is of frequent occurrence: according to Cuvier it is normal in the kangaroo, and other marsupial animals; and Tiedemann has observed it in some of the quadrumana, as the Lemur gracilis. So frequently is it met with in the human subject, that Dr. Barclay says we can scarcely call it an anomaly. Four cases, all differing from each other, were noted by me during the season, and I shall briefly describe them from the drawings which I took at the time. In the first, the bifurcation was about two inches above the bend of the elbow. The ulnar artery, instead of pursuing its deep-seated course, as is usual in the high division, passed superficial to the pronators and flexors, covered only by the palmaris longus, fascia, &c.; and, instead of giving off the interosseal, the radial supplied that artery, which reminds us in some degree of the type in birds, where the radial, after supplying the muscles about the radius, is lost in the interosseal arteries. The second case was similar, except that the ulnar passed immediately under the fascia over all the muscles. In the third, the bifurcation took place immediately after the origin of the superior profunda, and in this example the brachial plexus was posterior to the axillary artery*. The fourth and last case was the most remarkable, and is of rare occurrence. The brachial divided at its origin; the internal or ulnar branch, larger and deeper seated than the external or radial, after giving off the profunda and three small muscular arteries, communicated with the radial by means of a transverse branch, which crossed the tendon of the biceps. An inch and a half below this, the interosseal arteries proceeded separately from the ulnar; the lower one, the anterior interosseal, as large as the radial, gave off a median branch,which, piercing the median nerve, accompanied it down the fore-arm, and, becoming superficial towards the carpus, passed under the annular ligament, to terminate in two muscular branches for the thumb: no superficial palmar arch; digital arteries of index finger and external side of the middle finger supplied by the radial, as it was about to form the deep palmar arch: the other digitals proceeded from the ulnar. This irregularity, with some modifications, has been observed by Tiedemann, Meckel, and Green, and the last remarks that the transverse communication is only to be met with in the high, or axillary, bifurcation. The median branch sometimes comes from the transverse one, and forms the palmar arch with the ulnart. In This disposition of the nerves I have met with on three occasions during the season. one, the arteries were regular. Before I leave the upper extremity I may mention a case where the superficial palmar arch was deficient, and the ulnar supplied all the digital arteries, except that of the external side of the index finger, which proceeded from the radial. This variety is by no means frequent; it assimilates the type in birds where there is no palmar arch, and the ulnar is the principal trunk for the wing. The arteries on the left side were regular. With the exception of one example, I have not taken notes of any varieties in the abdominal arteries. They are of very frequent occurence, but of no practical importance. In the case of which I have taken a drawing, a second hepatic artery proceeded from the aorta, about an inch below the coeliac axis, and passed under the vena porta to reach the right extremity of the transverse fissure, where it supplied a cystic branch. The regular hepatic divided as usual. The above distribution is, I believe, rare. I shall now describe two very unusual varieties in the obturatrix artery, connected with equally remarkable ones of the epigastric. In the first, of which I have preserved a drawing, the obturatrix arose from the external iliac, above Poupart's ligament, and coasting along the anterior margin of the crural ring (in the centre of which it gave off at right angles considerably smaller vessel, which proved to be the epigastric,) descended into the pelvis to reach its destination. About a quarter of an inch before its exit from that cavity it gave off the dorsal artery of the penis, which, running along the side of the prostate gland, pierced the triangular ligament a little above the urethra, and sent off the artery of the crus. The pudic of this, the left, side terminated in the artery of the bulb. The vessels on the right side were perfectly regular. I need not here mention how formidable such a case would be for the lateral operation for stone, as also the danger of operating on such a patient for crural hernia. The above is of exceeding rare occurence; it is the first instance I have seen of it. I distinguish it particularly from examples of the obturatrix arising from the epigastric, which was to be seen frequently during the season in our dissecting rooms, and must be familiar to every anatomist. In one of the many cases of the ob+ The above irregularities existed on both sides. turatrix proceeding from the epigastric which came under my notice, I remarked a very peculiar course of the epigastric vein. This vessel, of considerable size, passing downwards and outwards at some distance internal to the artery of the same name, crossed the gland in the crural ring (dividing the opening as it were into two) to reach the internal side of the external iliac vein. If a crural hernia occured in such a subject as this, and if the sac passed between the epigastric and external iliac veins, we should be in danger of dividing in our operation, not only the obturatrix artery, but also a vein rendered of peculiar importance by joining so large a vessel as the external iliac vein. I have preserved a drawing of this. Besides these varieties I have seen one instance during the season of the epigrastic and obturatrix arteries arising from the femoral about half an inch below Poupart's ligament, and it was remarkable that the former, instead of ascending directly from its origin, first formed that arch downwards which it usually does. The obturatrix passed upwards on the pectineus behind the gland in the crural ring, and descended into the pelvis. Meckel states this variety to be very rare, and Tiedemann has seen but two cases of the epigastric proceeding from the femoral. Although the epigastric artery sometimes varies in its point of origin, I believe it is seldom found to deviate with respect to its relative anatomy. I have seen but one instance when it was not subjacent to the transversalis fascia in its course up the abdomen, and in that remarkable case, which occurred early in the season, it passed through a distinct opening in that fascia immediately after its orgin from the iliac, and remained superficial to it in its course upwards and inwards*. Irregularities of the femoral artery are fortunately of rare occurrence. In the 4th volume of the Dublin Hospital Reports a very interesting case of high division of the femoral and union within the tendinous canal, has been recorded by Dr. Houston, and the preparation may be seen in the College Museum. I have but two cases connected with this vessel to mention. Of the first I have made a preparation for the School Museum. It was an instance of an unusual size, origin, and, I may add, distribution of the external circumflex, which arose from the femoral under cover of Poupart's ligament, about a quarter of an inch below the circumflexa ilii, and passed down external and parallel to the parent trunk for about four inches; it then bifurcated under the rectus muscle into muscular branches. The proper circumflex vessels came off at its centre. In such a case we would be very liable to mistake the circumflex for the femoral in cutting down for the latter, more especially as the former was quite as large as the profunda, which, it may be well to state, came off from the crural as usual. In the second, the profunda arose from the femoral about an inch below Poupart's ligament, and ran external to it for about two inches. Besides this, five irregular branches of considerable size come off from the crural, almost equidistant from each other, before it reached its fibrous canal. Here two points occurred for consideration: first, the liability of taking the profunda for the femoral in the operation first alluded to; and secondly, even though we should secure the proper trunk, the danger of secondary hæmorrhage occurring if the neighbourhood of a considerable branch to the point of ligature can really be the cause of such. I put the point hypothetically, because I believe considerable doubt now exists on the subject; and I may adduce, as bearing on the question, a case in which the carotid was tied with perfect success by Professor Porter immediately at the starting off of the subclavian. It is most probable that an internal coagulum would not form in such a case, but we have no grounds for concluding that our success should be interfered with in consequence of its absence. It is true that operations have been said to have failed because of the neighbourhood of a large branch to the point of ligature, but when we come to consider the many causes of failure which may escape our notice, it is after all very difficult to settle on the true origin of the failure. I shall conclude by describing a distribution of the parts in the popliteal space, such as I have not before met with: a very correct drawing of it, which is in my possession, (which I hope soon to place before the profession, with other * L'artère (epigastrique) est constamment sketches,) represents the gastrocnemius placée derrière le fascia transversalis."-Velpeau, Surg. Anut. with three heads; the superadded one |