It is not necessary to specify which Gray or even to state the title of his book, although I may note that the date of my own copy is This young man, for he died when he was only thirty-five, bequeathed a real legacy to almost every English-speaking doctor who has studied medicine since his time.
A doctor may throw away his Bible, but he always keeps his Gray. In spite of the convenience it would be to have the standard facts of anatomy at hand, most purchasers of this book would probably prefer to have it published at less expense and to let them refer when necessary to the "Gray's" which they themselves have already thumb-marked.
Yet I know that when I read about a subject in which I am only half interested, I do not bother to use reference books as I should, and probably do the author an injustice by not being sure of the fundamental facts which he assumes I know, but which I have in truth forgotten.
The other extreme would be to assume that every doctor who may read this book already knows the standard anatomic structures of the shoulder, so that the whole chapter could be omitted. This alternative cannot be accepted because it is highly probable that even the graduating classes of the best medical schools could hardly qualify in this respect. Later, as year by year passes after graduation, our anatomic memories are crowded out by other more vital ones, so that it is very unlikely that half the fund of knowledge acquired by early anatomic instruction persists a decade.
After two decades of practice, any surgeon will admit that he has forgotten such matters as the branches of the brachial plexus or the origin and insertion of the levator anguli scapulae.
Even if my readers know all the well-recognized facts about anatomy, I should still have to write a chapter on the subject to accentuate the proportionate values of certain points which appeal to me. Moreover, there are a few undescribed facts which I need to present. Obviously compromise is necessary for I can neither assume that my readers know their anatomy nor wish me to repeat every detail which they may turn to in their text books. Nevertheless, to do justice to me they should refresh their memories, and for this purpose a list is presented of all the terms which concern the shoulder used by Gray in my own worn edition.
By running his eye over this list the reader may detect the weak spots in his own memory and, if he pleases, can turn to his Gray and revivify them. I beseech him to do so. Moreover, since this book is written quite as much for the coming generation as for my own and the present one, this list is presented in three columns so that it may serve as a glossary to all three generations.
It appears that the professors of anatomy intend that future medical students in all countries shall be taught the international Basle Anatomic Nomenclature. The writer believes that numbers 2, 3, and 4 of the above list are essentially one bursa, although they are often separated by thin, movable films of tissue. He believes numbers 5 and 6 to be really extensions of the joint as is also the synovial lining of the bicipital canal, number 18 in Fig.
The bursas numbered 9, 10, 11, 12, in the same diagram, are inconstant and have no official anatomic names. Even if you have satisfied your mind that each term in the B.
The shoulder. In descriptive anatomy there are no more sharp lines of distinction separating the regions called the shoulder, the neck, the back, the chest, the upper arm and the armpit, than we indicate in our ordinary uses of these words. Even the bones which compose its skeletal support cannot be sharply defined. Does the upper end of the humerus belong to the shoulder? Anatomists are accustomed to say no, and describe it with the arm. Surgeons certainly think of the upper end as a part of the shoulder, but would have no distinct lower limit.
We shall include the upper end of the humerus above the deltoid tubercle, and leave the other limits still somewhat vague. The shoulder girdle is not a complete girdle because the clavicles are separated by the manubrium top of the sternum in front, and the scapulae do not quite meet behind.
In birds the clavicles do meet and form the wish bone, In fact, "girdle" means the two bones of one side only, so it takes two shoulder girdles to not quite girdle the body.
It means for man the two bones which form a saddle for the arm to ride on the body, i. Did time and space permit, it would be instructive to discuss the comparative anatomy of the shoulder in the lower animals, for in different species there is great variation in the relative sizes and shapes of the muscles and bones and even in the proportions of the three component parts of the scapula itself.
Most animals have only a trace of the acromion process which in man and in the monkey is extremely well developed, probably to stabilize the joint for its many newly developed uses. So far as I know, no one has yet attempted to study the reasons which have led to the development of the variations of the different parts of the human scapula.
Possibly I was the first to draw attention to a fundamental difference between the human and the quadruped mechanism in the use of the forelimb; i. Man lifts Weight with a long lever. I hope to convince the reader in later chapters, that rupture of this muscle in man is almost equivalent to dividing the hamstring in an animal. If man walked on his forelegs, patients with this lesion would limp pitiably and get much more sympathy than they do now when they can only allege that they cannot raise their arms.
At any rate, from a mechanical point of view, man's ambitious change to the upright position resulted in a new form of shoulder joint. He has a relatively large and powerful acromion process to act as the mast of a derrick, to which his enormously developed deltoid is attached, and under which a relatively small supraspinatus is chiefly useful in holding the boom humerus on the fulcrum the glenoid.
We are proud that our brains are more developed than those of animals; we might also boast of our clavicles. It seems to me that the clavicle is one of man's greatest skeletal inheritances, for he depends to a greater extent than most animals except the apes and monkeys, on the uses of his hands and arms. The clavicle holds the shoulder away from the body and therefore permits us to use our arms with power and skill in abduction and adduction to a degree which few animals except the monkeys can approach.
The gorilla's shoulder girdle is as well if not better developed than man's. Some of the lower monkeys have less developed ones resembling those of the quadrupeds, but all have clavicles. I have never had the opportunity to dissect a gorilla, but he must have a well-developed subacromial bursa. Our relative also has a good clavicle, which seems small in this figure because it is foreshortened. Like a human clavicle it is S-shaped. Mammals that specialize in swimming e.
Even the carnivorous cat tribe lions, tigers, leopards and the domestic cat have only rudimentary or very small collar bones. In the bats, the clavicles are long and curved like those of birds. Moles have short, almost cuboid bones which are homologous with the clavicle, combined with the coracoid. Those species which do have clavicles appear to be flyers or climbers. Some of the rodents which climb trees—for instance, squirrels, have them.
Other rodents have none whatever. Curiously enough, some of the more ancient but waning species, such as the duckbill platypus, kangaroo, opossum and armadillo, have well-developed clavicles. Furthermore, the armadillo has the longest known acromion process and very few other animals have any to speak of. It appears that the acromion is developed in this animal to aid in carrying his shell.
The beaver has the most highly developed clavicle of any four-footed animal that I know of. His skeleton is also notable because he has a well-developed acromion process and a large deltoid tuberosity. His shoulder girdle is the best instance I can find for my theory that animals with strong clavicles use their arms in adduction and abduction, for the beaver's mechanical skill in building his huts and constructing his dams is well known.
Bears are my worst examples, for bears are clever in climbing, and yet have no clavicles. The sterno-clavicular joint. Any one can easily feel the joint where his clavicle touches the top of his sternum and realize that this is the only point at which the weight or power of his shoulder can get direct support from the rest of his skeleton when he pushes with his arm. And yet after removal of the clavicle, a man has pretty good use of his shoulder just as do horses and dogs who have no clavicles.
The acromio-clavicular joint. One can feel this at the other end of the clavicle and realize that this, too, must through its small surface transmit power or weight. One can also feel that the clavicular side is higher than the acromial side of the joint. It is an important fact. When one looks at the clavicle from above, one sees no joint surface, but when one looks at it from below one sees a j oint surface at each end.
This provides for upward displacement at either extremity, and therefore we never find downward dislocation of either end of the clavicle. The coracoid process is in shape and size much like a crooked forefinger projecting forward from the neck oi the scapula just as the acromion process projects back of the joint. The outer end of the clavicle crosses it transversely and is very firmly united to it by the coraco-clavicular ligaments which one cannot palpate because they are wholly underneath it.
One can just feel the end of this process below the outer end of the clavicle. It seems to be a part of the head of the humerus, but by rotating the latter, one may note motion between the two. The acromion process. This forms the whole of the posterior part of the top of the shoulder, while the head of the humerus makes the rounded forward outline.
The acromion extends well behind the articular head and the plane of its broad end is obliquely downward and backward and outward. Notice on your own shoulder how you can put your finger under the back of it. Notice that you cannot, with a club, hit a man from above or from behind on the top of his humerus, for the acromion is always in the way.
If the arm is raised, flexed forward or abducted; i. If his elbow is drawn backward, you could, from in front, strike on the front of the top of the tuberosities but not on the articular cartilage. This is a very important anatomic point for the surgeon, for only when the arm is in dorsal flexion can one feel the gap where a supraspinatus tendon has been ruptured.
It also leads to the conclusion that histories are unreliable which claim an injury to the top of a humerus from a fall or a blow. One cannot fall on the top of one's humerus, or strike any one else on the top of his humerus. The inner contour on which the thumb naturally comes when the shoulder is grasped is formed by the tip of the coracoid. The forefinger sinks under the edge of the acromion.
Notice that part of the facet for the infraspinatus lies in front of that of the supraspinatus, and compare with Fig. The position of the bicipital groove varies with the degree of rotation of the arm. Try this grasp on your own shoulder and rotate the humerus with the elbow flexed to a right angle. Bear in mind that the bicipital groove lies just outside of the median line of the upper arm in the anatomic position.
The spine of the scapula is the long base of the acromion and there are two little bony lumps on its lower edge which one can always feel and which are very useful as measuring points. The dorsal surfaces of the acromion and of the spine of the scapula are subcutaneous ; i. Evidently the ridge which they form was made to be hit; i.
Consider the mechanics of its structure and notice how it, with the clavicle, forms a movable arch over the vessels and nerves of the arm. This arch flaps like a wing as you hunch your shoulder and lower it, or abduct your arm and lower it. Observe also that the spine of the scapula rises between the supra- and infraspinatus to give attachment to the superficial layer of great muscles, i.
The two sets of muscles would be separated by sawing through the spine of the scapula. See Fig. The arch formed by the coracoid, the coraco-acromial ligament and the under side of the acromion is a hemispheric dome under which the hemisphere formed by the musculo-tendinous cuff and by the tuberosities exactly fits.
Under this arch the head of the humerus can move many degrees in all directions by the aid of the subacromial bursa. The reader must understand that the dissection pictured above is quite artificial. Such a capsule does not exist unless made at the expense of the musculotendinous cuff, a section of which is shown in Fig. One should try to visualize Fig. The glenoid is the shallow cartilage-covered surface where the head of the humerus obtains its fulcrum as the arm is raised.
Notice that the plane of its surface is at no particular angle with the rest of the scapula, for it faces somewhat forward and upward, and outward. Notice its narrow superior portion. The blade. The upper portion of the blade of the scapula from the lateral view forms in most people an obtuse angle with the rest of the blade so that it can fit over the curve of the upper ribs at the base of the neck.
Thus the thin blade of the scapula when pressed forward from behind fits nicely over the back of the upper seven ribs. Furthermore, the bony structure of the scapula is beautifully arranged to distribute force applied from behind.
The clavicle is a strut which connects the rest of the shoulder with the skeleton. It prevents the upper portion of the shoulder from jamming up against the rest of the body. In other words, the clavicle acts as does the iron rod a man uses to hold a bull who has a ring in the end of his nose. The clavicle is capable of a limited degree of circumduction, which is facilitated by the double joint at the sternal end.
Circumduct your whole arm with the forefinger of the opposite hand on the outer tip of the clavicle and you will find that the latter passes through an irregular circle about three inches in diameter. The clavicle is the boom of a derrick the neck and enables the trapezius to raise the whole shoulder. The ligaments. It is well to distinguish four kinds of ligaments which occur about the shoulder.
The coraco-clavicular ligament composed of conoid and trapezoid portions is a very typical example. There are three of these related to the shoulder; a very typical one in the sterno-clavicular joint; a less typical, often rudimentary one in the acromio-clavicular joint; and the glenoidal labrum which encircles the glenoid cavity and makes it slightly deeper.
In the shoulder there is such a ligament crossing the suprascapular notch through which the nerve and vessel pass. The transverse humeral ligament which makes the bicipital groove into a canal to restrain the long tendon of the biceps, is another. The coraco-acromial ligament is one of this kind, and we must speak of it in more detail. The coraco-acromial ligament will be mentioned again and again in this volume. It is wholly a scapular ligament, passing between the two processes from which it takes its name which are parts of one bone.
Its under surface forms most of the posterior part of the roof of the subacromial bursa, and the tuberosities of the humerus pass upward underneath it when the arm is elevated. It lies between the bursa and the acromio-clavicular joint. Its function appears to be largely to restrain the head of the humerus from gaining a fulcrum on this joint or on the under side of the end of the clavicle.
It is more elastic than bone but quite firm. Evidently the coraco-acromial ligament has an important duty and should not be thoughtlessly divided at any operation. One always finds it if the bursal incision is carried upward. The bursa, with this ligament and the two bones to which it is attached, really forms a secondary shoulder joint.
The other ligaments with simple but confusing names—the acromio-clavicular and the sterno-clavicular —surround their respective joints and pass between two different bones and have the functions usual in other joints.
We have already spoken of the coraco-clavicular ligaments p. The coraco-humeral and gleno-humeral ligaments should never have been described as entities. They are merely somewhat variable parts of the joint capsule. The muscles. I have few particular comments to make about the muscles which seem to be easier to remember from our student days.
Try this. Learn anatomy faster and remember everything you learn. Flex the arm at the glenohumeral shoulder joint. Nerves to the muscle :. Nerve roots :. Related Articles. The bands merge together as they approach the insertion point on the deltoid tuberosity of the humerus. The deltoid has three distinct functions that correspond to the three bands of muscle fibers. Contraction of the anterior fibers flexes and medially rotates the arm by pulling the humerus towards the clavicle.
Flexion and medial rotation of the arm moves the arm anteriorly, as in reaching forward or throwing a ball underhand. The lateral fibers abduct the arm by pulling the humerus toward the acromion. Abduction of the arm results in the arm moving away from the body, as in reaching out to the side.
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