1. Deficiency And Excess Of Development

In very incompletely-formed monsters no muscles whatever, or merely a few traces of them, are to be found. Not unfrequently, when that portion is imperfectly developed, a few, or the whole, of the muscles of some portion of the body are wanting. This is the case with the thoracic and abdominal muscles, and those of the back, when the thorax, abdomen, or spine is fissured; or with the muscles of a limb, when the development of its skeleton is arrested; and some supernumerary limbs, which do not pass beyond a rudimentary state, never have muscles formed in them. A few rare instances occur in which most of the muscles of a limb are wanting, although its skeleton is perfect. And now and then a few unimportant muscles, or parts of muscles of the face, trunk, or limbs are missing, but the want of them does not interfere with the power of motion in the part.

Allied to these instances of deficient development, in which one or more muscles are entirely absent, there are others in which a muscle may be imperfectly developed in bulk (thickness and power), and in texture. Sometimes one of its extremities is but partially formed, or not at all: or it may have no insertion, as is the case with muscles and their tendons at the stump of rudimentary limbs, or when, in the absence of the lower jaw, the muscles of the cheek are fused together with those of mastication. And, lastly, it may happen, that whilst the bony part of a limb is properly formed, the muscles are too short.

The form in which an excess of development presents itself is that of an increased number of muscles. Sometimes unusual ones exist, at other times a muscle has an irregular or accessory head, or an additional tendon; and, occasionally, particular parts are stronger than usual, and are separated by unnaturally deep fissures into independent muscles. In the same class may be included cases in which muscles and their tendons exceed the natural length.

2. Deviations Of Muscles From Their Natural Condition In Respect To Size Or Volume, And Form

Some of the examples of originally faulty development which have been mentioned in the last section, belong to the present also; but there are other anomalies which, though sometimes congenital, more frequently occur after birth, and are, therefore, more properly arranged in this section: the anomalies in question are those of shortening, atrophy, and hypertrophy of muscle.

In shortening (retractio, contractura) the muscular fibres are permanently contracted: the cause of their contracting is excessive innervation, and the consequence is gradual wasting of the muscle. It leads to a proportionate deformity of the skeleton of the part, which becomes permanently straightened or bent, and has its articulations partially or completely dislocated, and the bones themselves curved and bent. Whether it be congenital or come on after birth, it is a result of repeated tonic cramp. It is seen in wry neck, in club-foot and hand, in several of the curvatures of the spine, etc.

The circumstances under which atrophy of muscles takes place are various; sometimes it is a simple wasting, at other times a complicated. The former kind is distinguished by the muscular structure being paler than natural and easily torn, and is general throughout the whole muscular system; it is a consequence of advanced age, and of various diseases, and is found with gelatinous softening of the stomach and intestines in children, in the phthises, especially tubercular phthisis, in cases of extensive cancerous growth and cancerous degeneration, and in consequence of slow poisoning, especially with lead. An atrophy of the same kind ensues, but is more partial in its extent, when particular groups of muscles have been insufficiently used, and in paralysis. In some muscles it is brought on by the gradual pressure and distension which they suffer from the enlargement of organs, the dilatation of cavities, or from morbid growths: as by an enlarged thyroid gland, dropsical distension of the cavity of the peritoneum, aneurisms, sarcoma, cancers, etc.

A complicated atrophy of muscle is that in which the texture of the fibre is changed. Contracted muscles waste in this manner: they lose their natural color, and become first of a pale yellowish-red, then of a fawn, and lastly, of a dirty white color; while at the same time they degenerate into a firm, tense, fibrous (fibroid) cord. Muscles which are absolutely unused, such as those of anchylosed joints, waste and degenerate into fat. Moreover, the muscles are generally found atrophied when much fat is formed in the body.

A remarkable form of atrophy has been described by Mayo, which in two cases that came under his care, was brought on by long-continued exposure to cold, was attended with much pain, and ran a very acute course. It is a subject on which further investigation is still required; and in order to direct the attention of medical men and pathologists to it, I introduce here the second of Mayo's two cases.

A laborer, set. 45, who had been much exposed to wet, and was in the habit of allowing his clothes to dry upon him, was attacked, four months before he was seen, with pain in the left shoulder, which continued almost uninterruptedly for six weeks. It was most severe about fourteen days after it commenced, and still became sometimes so violent, that it seemed, he said, as if his arm would drop off. There was neither swelling nor redness; nor was there any numbness or tension when the shoulder was pressed, but he felt great pain when he raised the arm with the other hand. Without that assistance, he could not lift it at all. About a week after the affection had begun, he noticed that the shoulder was wasting. As the pain subsided, the wasting gradually advanced, and at the time when he was examined, the deltoid, supra-spinatus, infraspinatus, and the two teres muscles appeared to be completely absorbed, or reduced to thin layers of membrane. The shoulder was free from pain and the joint healthy, but yet he was unable to lift the arm. There was no emaciation of the forearm or hand.

The muscular coat of the alimentary tube, and the bladder, are in some rare cases manifestly attenuated. Their walls become thin, transparent, withered, and pale. Sometimes an atrophied condition of the muscular coat of the alimentary tube is met with, analogous to that which is combined with the growth of fat; the muscular coat of the bowel becoming thin, at the same time that fat accumulates in the mesentery, the omentum, and throughout the system.