Part 5

25. =Cricoid cartilage.=--The projection of the cricoid cartilage is a point of great interest to the surgeon, because it is his chief guide in opening the air-passages, and can always be felt even in infants, however young or fat. It corresponds to the interval between the fifth and sixth cervical vertebræ. The commencement of the œsophagus lies behind it: here, therefore, a foreign substance too large to be swallowed would probably lodge, and might be felt externally.

Again, a transverse line drawn from the cricoid cartilage horizontally across the neck would pass over the spot where the omo-hyoid crosses the common carotid. Just above this spot is the most convenient place for tying the artery.

26. Those who have not directed their attention to the subject are hardly aware what a little distance there is between the cricoid cartilage and the upper part of the sternum. In a person of the average height sitting with the neck in an easy position, the distance is barely one inch and a half. When the neck is well stretched, about three-quarters of an inch more is gained. Thus, we have (generally) not more than seven or eight rings of the trachea above the sternum. None of these rings can be felt externally. The second, third, and fourth are covered by the isthmus of the thyroid gland. The trachea, it should be remembered, recedes from the surface more and more as it descends, so that, just above the sternum in a short fat-necked adult, the front of the trachea would be quite one inch and a half from the skin.

27. =Trachea.=--In the dead subject nothing is more easy than to open the trachea: in the living, this operation may be attended with the greatest difficulties. In urgent dyspnœa you must expect to find the patient with his head bent forward, and the chin dropped, so as to relax as much as possible the parts. On raising his head, a paroxysm of dyspnœa is almost sure to come on, threatening instant suffocation. The elevator and depressor muscles draw the trachea and larynx up and down with a rapidity and a force which may bring the cricoid cartilage within half an inch of the sternum. The great thyroid veins which descend in front of the trachea are sure to be distended. There may be a middle thyroid artery. In children the lobes of the thymus may extend up in front of the trachea, and the left vena innominata may cross it unusually high. Thus the air-tube may be covered by important parts which ought not to be cut. Considering all these possible complications, the least difficult and the best mode of proceeding is to open the trachea just below the cricoid cartilage; and if more room be requisite, to pull down the isthmus of the thyroid gland, or in children to divide the cricoid itself. It is important that all the incisions be made strictly in the middle line, the ‘line of safety.’

28. =Sterno-mastoid muscle.=--The sterno-mastoid muscle is the great surgical landmark of the neck. It stands out in bold relief when the head turns towards the opposite shoulder. Its inner border overlaps the common carotid, which can be easily compressed for a short time against the spine about the level of the cricoid cartilage. The artery extends (generally) as high as the upper border of the thyroid cartilage and corresponds with a line drawn from the sterno-clavicular joint to midway between the angle of the jaw and the mastoid process.

Between the sternal origins of the sterno-mastoid is the fossa above the sternum, more or less perceptible in different necks. As it heaves and sinks alternately, especially in distressed breathing, it was called by the old anatomists ‘fonticulus gutturis.’ In beautiful necks, as seen in the ‘Venus,’ it is filled up by fat.

Notice the interval between the sternal and clavicular origins of the sterno-mastoid. A knife introduced a very little way into this interval would wound, slanting inwards, the common carotid, slanting outwards, the internal jugular vein. These facts are of importance in performing the subcutaneous section of the tendon of this muscle.

29. =Sterno-clavicular joint.=--Many important parts lie behind the sterno-clavicular joint. There is the commencement of the vena innominata; behind this comes the common carotid on the left side, and the division of the arteria innominata on the right. Deeper still, the apex of the lung rises into the neck.

In a child the arteria innominata often lies in front of the trachea and divides a little higher than the joint: a point to be remembered in tracheotomy (27).

30. =Apex of lung in the neck.=--The extent to which the apex of the lung rises into the neck is greater than is generally supposed. Many observations in reference to this point lead to the conclusion that the lung rises behind the sterno-mastoid, on an average, one inch and a half above the clavicle; in persons with long necks, as much as two inches. The apex of the lung and pleura is covered by the clavicular origin of the sterno-mastoid, the sterno-thyroid, and a part of the scalenus anticus. It is also crossed by the subclavian vessels in the first part of their course. As this cervical portion of lung is peculiarly liable to tubercular disease, it should always be carefully examined. Its condition may be ascertained by percussion near the sternal end of the clavicle.

31. =Supra-clavicular fossa.=--The hollow above the clavicle, between the sterno-mastoid and the trapezius, is very manifest in emaciation and old age. Notice the termination here of the external jugular vein. In some necks only a small depression is visible, particularly when the trapezius has a broad insertion into the clavicle, and comes well forwards, so that its front border gives a graceful contour to the base of the neck.

32. =Subclavian artery.=--In the supra-clavicular fossa, near the outer border of the sterno-mastoid, and about one inch above the clavicle, we feel the pulsation of the subclavian artery. Here the artery lies upon the first rib, and can be effectually compressed. A little pressure is sufficient. But the pressure must be made in the right direction, or the artery will be pressed off the rib instead of against it. The plane of the rib is such that the pressure, to be effectual, must be made in a direction downwards and a little inwards. It is best to stand behind the shoulder and make the pressure with one thumb.

It is worth remembering that the outer border of the sterno-mastoid corresponds pretty nearly with the outer edge of the scalenus anticus, which is the surgical guide to the subclavian artery.

By pressing deeply at the upper part of the supra-clavicular fossa, the transverse process of the seventh cervical vertebra can be distinctly felt.

In long and thin necks, a thin cord is perceptible, running nearly parallel with and just above the clavicle. It is the posterior belly of the omo-hyoideus. See it rising and falling in breathing, and making tense during inspiration that part of the cervical fascia which lies over the cervical portion of the lung. Thus it may be said to be in all respects a muscle of inspiration, co-operating with the sterno-mastoid and scaleni. In the language of transcendental anatomy, we may say that the central tendon of the omo-hyoid represents a rudimentary cervical rib. Its posterior belly is analogous to a serration of the serratus magnus; its anterior belly to a sterno-hyoid.

THE CHEST.

33. As a rule, the right half of the chest is slightly larger than the left. Of ninety-two persons of the male sex and good constitutions, seventy-one had the right side the larger; eleven the left; ten had both sides equal. The maximum of difference in favour of the right was one inch and a quarter. The measurements were made on a plane with the nipple.

34. =Peculiarities in the female.=--The chest of the female differs from that of the male in the following points:--Its general capacity is less; the sternum is shorter; the upper opening is larger in proportion to the lower; the upper ribs are more movable, and therefore permit a greater enlargement of the chest at its upper part, in adaptation to the requirements of pregnancy.

35. The top of the sternum is on a level with the second dorsal vertebra; and the available space between the top of the sternum and the spine is hardly more than two inches.

36. =Parts behind first bone of sternum.=--There is little or no lung behind the first bone of the sternum, the space being occupied by the trachea and large vessels as follows:--

The left vena innominata crosses the sternum just below the upper border. Next come the great primary branches of the arch of the aorta. Deeper still is the trachea dividing into its two bronchi opposite the junction of the first and second bones of the sternum. Deepest of all is the œsophagus.

About one inch from the upper border of the sternum is the highest part of the arch of the aorta, which lies on the bifurcation of the trachea.

37. The course of the arteria innominata corresponds with a line drawn from the middle of the junction of the first with the second bone of the sternum, to the right sterno-clavicular joint. When the artery rises higher than usual into the neck, its pulsation can be felt in the fossa above the sternum.

38. =Rules for counting the ribs.=--In fat persons it is often difficult to count the ribs; hence the following rules may be useful:--

a. The finger passed down from the top of the sternum soon comes to a transverse projection, slight, but always to be felt, at the junction of the first with the second bone of the sternum. This corresponds with the level of the cartilage of the second rib.

b. The nipple of the male is placed, in the great majority of cases, between the fourth and the fifth ribs, about three-quarters of an inch external to their cartilages.

c. The lower external border of the pectoralis major corresponds with the direction of the fifth rib.

d. A line drawn horizontally from the nipple round the chest cuts the sixth intercostal space midway between the sternum and the spine. This is a useful rule in tapping the chest.