I presented, two years since, various general views upon the fibrous membranes, which have opened the way; but these membranes are only a division of the fibrous system, which must be considered here more at length.
ARTICLE FIRST.
OF THE FORMS AND DIVISIONS OF THE FIBROUS SYSTEM.
Though all the fibrous organs have precisely the same nature, and though the same fibre enters into the composition of all, yet the forms which they assume are extremely various; it is this variety of form, joined to that of their position and their functions, which has given them a different denomination, and made us designate them by the name of tendons, aponeuroses, ligaments, &c.; for there is no general denomination for the whole system, no word which answers for example to that of muscle, nerve, &c. which in the muscular, nervous systems, &c. gives an idea of the organization, whatever may be the form of the organ. I shall not create a word, I shall be easily understood without it.
All the fibrous forms can be referred to two general ones; one of these is membranous, the other in fasciæ. The organ is broad and thin in the first; it is longer and thicker in the second. Thus the muscles, the nerves, the bones themselves exhibit alternately this arrangement in their conformation, as we see in the retina compared with the round nerves, in the muscular layers of the stomach and the intestines, compared with the muscles of locomotion, and in the bones of the cranium compared with those of the extremities.
I. Of the Fibrous Organs of a Membranous Form.
The fibrous organs arranged as membranes are, 1st, the fibrous membranes, properly so called; 2d, the fibrous capsules; 3d, the tendinous sheaths; 4th, the aponeuroses.
1st. The fibrous membranes comprehend the periosteum, the dura-mater, the sclerotica, the albuginea, the peculiar membranes of the kidney, the spleen, &c. &c. They are in general destined to form the covering of certain organs, into the structure of which they enter.
2d. The fibrous capsules, very distinct, as we shall see, from the synovial surfaces, are a kind of cylindrical sacs, which are found around certain articulations, especially those of the humerus and the femur, whose connexions with the scapula and the ilium they strengthen, by embracing with their two extremities, both surfaces of the articulation.
3d. The fibrous sheaths are destined to confine the tendons in their passage upon the bones, where they are reflected, and generally wherever by muscular contraction they would be made to deviate and consequently transmit with difficulty to the bones the motion they receive from the muscles. They may be divided into two kinds; one receives and transmits the tendons of many muscles united, as is seen at the wrist, the instep, &c.; the other, like that of the fingers, is destined for a single tendon, or two only.