Tendons and Their Functions

Section VI. op TUB TBNDOirS. The tendons consist of that part of the fibrous system which is attached to the muscles. They are, with a few exceptions, attached on the one hand to those organs and on the other to the bones; a few of them are joined by both of their extremities to muscles, and thus placed in their substance; these, which are called tendines intermediae, are met with in the digastric muscles. The forms of these bodies are various, most of them consist of elongated cords, which are usually flattened or rounded; these are the tendons properly so called; others amongst them, which are broad and membranous, are described by many anatomists with the aponeuroses, under the name of aponeuroses of attachment. Some of the tendons have the form of arches; an arrangement which is admirably adapted to give passage to blood-vessels, in such a manner as to avoid injurious pressure when the muscles contract; the transmission of the aorta through the diaphragm, is a striking illustration of this mechanism. It frequently happens that a tendon has the form of a cord for a considerable part of its extent, and then at one or both of its extremities, becomes expanded into a membrane. Sometimes a single tendon divides into several others, which pass separately to their insertion; this is the arrangement in the flexor tendons digitorum pedis; and in other instances, two tendons unite to form one, as in the junction of the gastrocnemius, where they produce the tendo Achilles. <Callout type="important" title="Important">Every tendon in the body is intimately connected by one of its extremities with the muscular fibres.</Callout> By the opposite extremity, the tendon is inserted into the bones, and usually near their articulations; in a few instances the insertion is placed in an aponeurotic, membranous, or cartilaginous body. Some of the tendons which are exposed to great friction, are converted into a fibro-cartilaginous and even into an osseous texture; such are those of the peroneus longus and tibialis posticus.<Callout type="risk" title="Risk">These tendons can become brittle and prone to injury due to constant friction.</Callout> The tendons are usually secured in their situation by the aponeuroses and tendinous sheaths; and in these places they are covered by synovial bursae. They also possess bursae mucosse where they play against the bones and cartilages, and where they rub against each other. Elsewhere they are surrounded by loose cellular tissue. The force of cohesion and the want of extensibility enable the tendons to perform the only office they are destined to fulfil, viz. that of transmitting to the bones the action of the muscles.<Callout type="tip" title="Tip">Regular stretching can help maintain tendon flexibility.</Callout> 362 Fibro-Cartilages. Chapter Eighteen. Of the Fibro-Cartilaginous System. The character of the different parts which compose this system, are intermediate to those of the two preceding systems; and in consequence of this circumstance, some anatomists have described them as cartilages, whilst others have considered them as ligaments. Many of them appear to be modifications only of the latter organs, and therefore in the table of the solids I have included them under the general denomination of the fibrous tissue.<Callout type="gear" title="Gear">Specialized medical tools can help diagnose tendon issues.</Callout> It is evident that Galen had noticed some of these bodies, which he called neuro-chondroid ligaments. Vesalius also regarded them as ligaments. On the contrary, Haase described them as cartilages, and divided them into the ligamentous cartilages, cartilagines ligamentostea, and the mixed cartilages, cartilagines mixtae. The fibro-cartilages were subdivided by Bichat into three classes: — Ist. The membranous, including those of the ear, the nose, the eyelids, the wind-pipe, the bronchi, etc. 2d. The articular, which are either free on both their surfaces, as in the articulation of the knee, of the lower jaw, etc.; or intimately attached on both sides, as those placed between the bodies of the vertebrae. 3d. The fibro-cartilages of the tendinous sheaths, which * See p. 7a are met with in the places where tendons rub against the periosteum; for example, the tendons behind the inner ankle.<Callout type="important" title="Important">The fibro-cartilages play a crucial role in maintaining joint health and flexibility.</Callout> In the more recent works of Béclard and Meckel it is objected that the organs of the first class belong to the proper cartilages, and ought, therefore, to be omitted; and that it is necessary to add the ligamento-fibro-cartilaginous bodies, which are found around some of the end-joints. Béclard also includes in the system we are now considering certain fibro-cartilages in which some of the bones, as the patella, are formed.<Callout type="risk" title="Risk">Improper handling or lack of knowledge can lead to misdiagnosis and ineffective treatment.</Callout> It must be admitted that several of these alterations are judicious; but with respect to the fibro-cartilages of the ears, nostrils, etc., I believe their peculiarities are sufficiently marked, to distinguish them from the true cartilages.<Callout type="tip" title="Tip">Understanding the structure and function of tendons can aid in injury prevention.</Callout> The fibro-cartilaginous organs may be referred to two classes, the temporary and the permanent. Those of the first order, which are called the fibro-cartilages of ossification, pass regularly and at determined periods, into the osseous state. They are met with in the substance of tendons and ligaments; they are purely fibrous in the principle, but afterwards become fibro-cartilaginous, and ultimately osseous. The patella and ossa sesamoidea are developed in this manner.<Callout type="gear" title="Gear">Ultrasound can be used to visualize tendon structure for better diagnosis.</Callout> Bodies of a similar nature are constantly formed in tendons which rub against bones, ex. gr., the gemellus against the condyles of the femur, and the peroneus longus against the os cuboides; they are also contained in certain ligaments, as in the stylo-hyoid and thyro-hyoid.<Callout type="important" title="Important">The development of fibro-cartilages is crucial for joint health.</Callout> The permanent fibro-cartilages require to be subdivided into three classes: — 1. Those which have more or less the form of plates or rings. 2. Those of the articulations. 3. Those of the tendinous sheaths.<Callout type="important" title="Important">Understanding these structures can aid in injury prevention and treatment.</Callout> I. The first class comprehend the fibro-cartilages of the ear, nose, and eyelids; the median fibro-cartilage of the tongue; the epiglottis and the fibro-cartilages of the larynx, trachea, and bronchi.<Callout type="risk" title="Risk">Ignoring these structures can lead to ineffective treatment.</Callout> Although these exhibit variations in their density, so that some of them as those of the larynx and septum narium are finer than those of the auricle and alae nasi, yet all of them are more flexible, less fragile, and more tenacious than true cartilage. The solidity and elasticity which they possess, enable them to maintain the shape and cavity of the canals and other parts which they assist in forming.<Callout type="tip" title="Tip">Regular check-ups can help identify issues with these structures early.</Callout> The majori^ of them are closely covered by dense membrane, called perichondrium, which is similar to the investing structure of cartilage; and several amongst them are lined by the mucous membrane.<Callout type="gear" title="Gear">Specialized imaging can help diagnose issues with these structures.</Callout> Some of the fibro-cartilages of this class are intimately joined to the neighbouring bones; as, for example, those of the nasals and of the external auditory canal; others, on the contrary, are only attached by membranes in muscles, as those of the eyelids and of the larynx.<Callout type="important" title="Important">Understanding these connections can aid in injury prevention.</Callout> The latter organ is also distinguished by the mobile and perfect articulations, which are formed between its component parts; and farther, by the very sudden development of those parts at the time of puberty.<Callout type="risk" title="Risk">Ignoring these developmental changes can lead to misdiagnosis.</Callout> II. The articular fibro-cartilages are of three kinds: a. Those which have two free surfaces, usually called the inter-urticulur cartilages. They are placed in joints which are exposed to great friction or to severe shocks, as in the joint of the knee, in that between the ulna and radius, etc., the temporo-maxillary, sterno-clavicular, and sojoints in the gomulo-clavicular articulations.<Callout type="important" title="Important">These structures play a crucial role in reducing friction within joints.</Callout> Each of these bodies is covered on both surfaces by the synovial membrane, and the borders are united by a fibrous texture to the ligaments, or to the articular cartilages. They are very elastic, and in most instances they also moveable, and being thus enabled to change their situation according to the motions of the joint, they powerfully assist in diminishing the compression that would otherwise be experienced.<Callout type="risk" title="Risk">Ignoring these structures can lead to increased wear and tear on joints.</Callout> b. The fibro-cartilages placed around the cotyloid and glenoid cavities, which are composed of circular fibers; they are covered on the inner side by the synovial membrane, and on the outer by the fibres of the capsule.<Callout type="important" title="Important">These structures help maintain joint stability while allowing for flexibility.</Callout> They deepen the sockets of the above joints, and so increase their strength; whilst, in consequence of their flexibility and elasticity, they do not so much restrict motion as if their place had been supplied by an unyielding osseous matrix.<Callout type="risk" title="Risk">Ignoring these structures can lead to joint instability.</Callout> c. The fibro-cartilaginous substance which is placed in the immovable and mixed articulations.<Callout type="important" title="Important">These structures play a crucial role in maintaining joint stability.</Callout> It is met with in the sutures of the head, in the pubic and sacro-iliac symphyses, and between the bodies of the vertebrae. This elastic matter adheres firmly to the bones between which it is placed; and on the outer surface it is covered either by the pericranium or by strong ligaments.<Callout type="risk" title="Risk">Ignoring these structures can lead to joint instability.</Callout> III. The fibro-cartilages of the tendinous sheaths are formed where tendons play against bones, in consequence of the periosteum being conducted by the continual friction; and also in those places where tendons rub against ligaments.<Callout type="important" title="Important">Understanding these structures can aid in injury prevention.</Callout> Ex. gr., The tibialis posticus against the calcaneo-scaphoid ligament- These structures adhere by one of their surfaces to the bones, and on the other they are covered by synovial membrane.<Callout type="risk" title="Risk">Ignoring these structures can lead to increased wear and tear on tendons.</Callout> The fibro-cartilages are composed of an intermixture of cartilaginous and fibrous substances. These materials form, in different proportions, alternate layers, which are readily distinguished from each other.<Callout type="important" title="Important">Understanding the composition of these structures can aid in diagnosis.</Callout> This disposition is particularly evident in the inter-vertebral fibro-cartilages; where the fibrous portion which predominates is arranged in white elastic and concentric layers, and between them the cartilaginous matter is placed; towards the centre there is a whitish pulp, destitute of fibres, and which is apparently v.generis. In the inter-uricular fibro-cartilages, and in those of the tendinous sheaths, the quantity of cartilage exceeds that of the ligamentous fibres, so that the latter are perceived with difficulty.<Callout type="important" title="Important">Understanding these structures can aid in injury prevention.</Callout> In other respects the organization of this system does not sensibly differ from that of the cartilages or of the fibrous organs. The chemical properties of these bodies have not been much attended to; but they appear to be intermediate to those of the two preceding systems.<Callout type="important" title="Important">Understanding these structures can aid in diagnosis and treatment.</Callout> Their physical properties resemble those of the ligaments and cartilages. Their tenacity or force of cohesion is very great, and in some instances it even surpasses that of the bones. They are highly elastic, and thus return promptly on themselves when they have yielded either to extension or to pressure.<Callout type="important" title="Important">Understanding these properties can aid in injury prevention.</Callout> The vital properties are very obscure. The permanent fibro-cartilages accomplish several uses. Some of them, as those of the ear, nose, larynx, etc., assist in the formation of very important organs; others give strength and elasticity to the joints in which they are placed; and lastly, there are several that perform the double office of ligament and cartilage, by strongly binding together certain bones, and, in virtue of their elastic property, by adding to the security of their articulations.<Callout type="risk" title="Risk">Ignoring these structures can lead to joint instability.</Callout> The temporary fibro-cartilages serve as the mould or type of the bones, whose place they supply. In the beginning of life these bodies are soft, and, according to Meckel, they have then a greater resemblance to cartilage than at a later period.<Callout type="important" title="Important">Understanding this development can aid in injury prevention.</Callout> Most of them in the first instance assume the fibrous form, but some pass at once from the gelatinous condition to their perfect state. The fibro-cartilages, with the exception of those of the larynx and the rings of the trachea, are rarely ossified in the advance of life.<Callout type="important" title="Important">Understanding this development can aid in injury prevention.</Callout> 08PINITI0N OP BOMBS. Chapter Ninth. Of the Osseous System. The osseous system consists of those hard parts of the animal frame which are called bones. They constitute in man and in all vertebrated animals, an internal skeleton, which determines the form and size of the body; they also give support to the soft parts, and receiving the attachment of the various muscles, they form with these, the organs of motion.<Callout type="important" title="Important">Understanding bones can aid in injury prevention.</Callout> The vertebrated animals have no internal skeleton, although many of them possess a hard calcareous envelope, which is usually called their external skeleton; but this structure bears more resemblance to the epidermis than to the osseous system of the vertebrata, for, like the epidermis, it is capable of being changed and renovated whenever occasion renders it necessary.<Callout type="important" title="Important">Understanding bones can aid in injury prevention.</Callout> Thus the lobster loses its shell every year, when the body has so much increased in size as to become too large for its former covering. In the vertebrated animals, on the contrary, the bones, in virtue of their organization, are spontaneously developed, and by a process of growth similar to that of the soft parts, they gradually enlarge, and attain their full perfection at the same time that the body reaches its maturity.<Callout type="important" title="Important">Understanding this development can aid in injury prevention.</Callout> There is no part of the animal economy that presents a more striking illustration of the Adaptation of parts to their particular uses than the osseous system. Perfection OP THE 9KBLBT0N. 369 This is apparent in the skeletons of various animals, which are constructed with a reference to their peculiar mode of existence.<Callout type="important" title="Important">Understanding this can aid in injury prevention.</Callout> In birds, for example, the principal bones are pierced by openings which, communicating with the lungs, admit air into their interior and in this manner add to their dimensions and strength, without increasing their weight. <Callout type="risk" title="Risk">Ignoring these structures can lead to reduced mobility and function.</Callout> The spermaceti whale, physeter macrocephalus, affords another instance of the great perfection of the skeleton.<Callout type="important" title="Important">Understanding this can aid in injury prevention.</Callout> This inhabitant of the deep, differing in this respect from other fishes, breathes by means of lungs; so that the animal is compelled to rise, from time to time, to the surface, in order to respire the atmospheric air. Now, to facilitate this ascent, the osseous cavities of the head are filled with spermaceti, a fluid specifically lighter than water, and consequently well calculated to render the head buoyant and to keep the blow-hole above the level of the sea.<Callout type="important" title="Important">Understanding these structures can aid in injury prevention.</Callout> If we extend our examination to the individual parts or the skeleton, we shall be struck with the same excellence and design pervading the form and arrangement of the several bones. Where everything is so perfect, it is difficult to make a selection; but what can be more admirable than the construction of the skull — of that wonderful piece of mechanism, which is provided for the reception of the brain? It possesses the globular form, which is, of all others, that best adapted to resist external violence; its various bones are fitted to each other with the nicest exactness, and with an evident relation to the great principles of architecture; and, lastly, to secure, in the most efficient manner, the safety of the brain, it is observed, that the cranium is strengthened in those parts which are exposed to injury, by the accumulation of osseous matter, and by the provision of resisting spines and tubercles.<Callout type="important" title="Important">Understanding this can aid in injury prevention.</Callout> The vertebral column, containing as it does a most important part of the nervous system, and constituting at the same time the common centre of the motions of the body, might be adduced as another example of the infinite wisdom displayed in the formation of our corporeal frame.<Callout type="important" title="Important">Understanding this can aid in injury prevention.</Callout> I shall have occasion, in another part of this chapter, to allude to the mechanism displayed in the articulations of the upper and lower extremities. I shall, therefore, for the present, quit this interesting branch of anatomy, which must always excite, in a well regulated mind, a powerful feeling of admiration and reverence.<Callout type="important" title="Important