Properties.—The offices which these organs are designed to fulfil in the economy being, with the exception of the periosteum and its analogous membrane the dura mater, of a me chanical character, the properties by which they are distinguished are almost entirely of a physical nature. They offer great resistance to rupture, and thus the ligaments are capable of opposing the shocks to which, in the violent movements of the joints, they are so frequently exposed; whilst the same cohesive property enables the tendons, under all ordinary circum stances, to bear the immense force of muscular contraction.
Having considered the general characters of these organs, I shall proceed to describe the most essential properties of each individual class.
1. Of the periosteum.—This may be regard ed as the most important of the fibrous tissues ; indeed so universal are its connexions, that if any common centre of this system were sought for, we should certainly coincide with Bichat in considering this to be the periosteum. Dis carding the erroneous ideas of the ancients and Arabian physicians, who imagined that the membranes of the body were all continued from those of the head, we shall find that, with the exception of the perichondrium of the larynx and the fibrous tunics of some glandular bodies, all the fibrous organs are in connexion with the periosteum.
The inner surface of the periosteum firmly adheres to the several bones by a multitude of delicate processes passing into the openings observed on their external surface. These pro cesses convey into the bones an amazing num ber of fine arteries and veins, called therefore periosteal, and which may be regarded as the principal, or as some anatomists contend, the only proper vessels of the osseous tissue.
The outer surface is rough, and is united by the cellular tissue to the surrounding muscles, tendons, ligaments, and fasciae; in the nostrils, sinuses, and tympanum, the periosteum is, however, joined to the mucous membranes, and in the skull the surface unattached to the bones is lined by the arachnoid.
The periosteum constitutes the nutrient membrane of the bones, and thus bears an im portant part in the process of ossification and in the reparation of fractured and diseased bones ; it also serves as a medium for the attachment of the ligaments, tendons, and fascire to the skeleton.
2. Fusciee.—The fibrous fascia: or aponeu roses not only invest the surface of the limbs, but also furnish a number of processes, which, penetrating deeply among the several muscles, form sheaths to those organs, by which they as well as the bloodvessels and nerves are main tained in their proper situation. It is evident
that these partitions must exert a great influence on the growth of various kinds of tumours, on effusion of blood, on the extravasation of urine, and on the formation of matter; so that their relations form an important branch of surgical anatomy.
In order to give to these muscular envelopes the necessary degree of tension, they are either provided with special muscles, as in the case of the tensor vaginae femoris and the palmaris longus, or they receive processes from the neighbouring tendons, as from the biceps cubiti, semi-tendinosus, and so forth.
The aponeuroses thus braced afford a firm support to the parts they cover, and in this manner they increase the powers of the muscu lar system ; whilst by their resistance they efficiently protect the vessels and nerves from external violence, and at the same time proba bly assist in the circulation of the blood and lymph, and so prevent varicose enlargement of the deep-seated veins and edema of the extre mities. See FASCIA.
3. Tendinous sheaths.—These are in their office analogous with the last, excepting that, instead of fixing the muscles, they secure the tendons during muscular action. The thecal ligaments of the hand and foot, the annular ligaments of the wrist and ankle, and the fascia' sheaths around the knee are of this character. They are distinguished by their great strength, and as they are internally lined by synovial membrane, they facilitate the play of the ten dons; and in many instances, as in the trochlea of the os frontis and the sulci of the carpal extre mity of the radius, they also modify the action of the muscles whose tendons they transmit.
4. Fibrous coverings.— Certain organs are provided, for the purpose of protection, with dense ligamentous coverings; of this order are the dura mater, the sclerotic coat of the eye, the loose portion of the pericardium, the proper covering of the kidney, of the salivary glands, mamma, spleen, thyroid gland, thymus, lym phatic glands, of the prostate, testicle and ovary; probably the exterior investment of the nervous ganglia is of the same character. Some of these envelopes, as the dura inater, pericar dium, and tunica albuginea testis, are lined on one surface by a serous membrane, and thus constitute jibro-serous membranes, or as they are called by Beclard, compound fibrous mem branes.