Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them]

Chapter 2 The Nature, Use, and Varieties of Cartilage

The nature of cartilage
CARTILAGE is softer than bone, but earthy, 1 and second to bone the hardest of the parts of the body, thoroughly solid, having no inner foramina [foramina nutrientia] or pores [es nutrientes] as bone does, and free of sensation or marrow.

Its use, similar to the ordinary use of bones
Its use is extremely varied. In the first place it performs the same function as bone, when it acts as a support to which neighboring parts are attached and stabilized. The cartilages of which the larynx is made, for example, elegantly perform the functions of bones: certain muscles are inserted into them, and several originate from them. Moreover, these cartilages form the larynx just as we see the houses of rustics are made of beams before thatching, tiles, and clay are applied to them. In fact, if you stripped bones and cartilages of their flesh and then joined them together, you would compare them to nothing more closely than the framework of huts when they are first erected and not yet covered with branches and earth. 2 In the same way, cartilages take the place of bones when they are placed where there is no bone and muscles are inserted in them. This happens in the eyelids and the nose. In the edges of the eyelids, there are long cartilages [tarsus superior et inferior] into which are inserted the muscles that move the eyelids [m.orbicularis oculi]. In addition to these, the alae of the nose are made of cartilages that take the insertions of muscles [m. nasalis, m. levator labii superioris alaeque nasi] exactly as bones. Indeed, those cartilages of the alae, 3 together with other cartilages growing out of the bones of the nose, 4 nicely support the apex of the nose just as if they were bone, and elevate it.

Cartilage is easier to contract and expand than bone
In addition, the bones of the ribs end in cartilages [cartilagines costales] which to all practical purposes correspond to the bones; but these also have a special function of permitting the size of the thorax (which they form together with the ribs) to be more easily expanded and contracted than if they were rigid and hard like bones. Also, for a similar purpose the cartilages of the rough artery [cc. trachiales] that look like our letter C differ from bones in that besides handsomely holding it up and performing the function of support, 5 they posses that blend of properties that allows

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them to be stretched and compressed unlike bone.

The use of cartilage in joints
Another, and by no means the meanest use of cartilage, is that it provides the bones the opportunity to be in continual and frequent motion with less wear from friction. The meeting-points [cartilago articularis] of bones that are built for movement would, because of the dryness of bones, be easily damaged from the mutual contact unless the total area of contact where they come together and form a joint were separately covered by cartilage as by a casing, and this cartilage by its mixture of hardness and softness resisted the impact of the bones, and by yielding slightly undid the force of their contact. Cartilage is suited not only for reducing the friction of bones where they are worn by mutual contact, but it is seen to be so smooth and even that the head of a bone very readily turns in its socket, 6 and no roughness impedes this ease of motion as long as there is present a viscous and slippery liquid [synovia] similar to the lubricant with which we coat the pulleys on which ropes are turned. 7

A third cartilage in certain joints
Indeed, the wise Maker of things recognized that there would be an outstanding use of cartilage in the joints, so he not only equipped the bones in the way we have described with a smooth and slippery casing of cartilage [cartilago articularis] at the point of mutual contact, but in several joints he also applied a third substance besides these cartilages, 8 which is attached to the cartilage of neither bone, but only to the membranous ligaments [capsulae articulares] of the joint [juncturae synoviales]; it is circular, and creates as it were an intervening space [cavitas articularis] between the cartilages covering the bones. This [discus articularis] is smooth on both sides where it lies between the other cartilages, and is slippery because of a viscous liquid [synovia] with which it is coated, and much softer than the cartilages that grow on the bones. You will learn in the appropriate place that cartilage of this kind [c. fibrosa] separates the joints of the lower maxilla to the upper [articulatio temporomandibularis]. Others separate the joint of the sternum with the clavicle [articulatio sternoclavicularis], the clavicle with the upper humerus [articulatio acromioclavicularis], the ulna with the carpus [articulatio radio-ulnaris distalis], and the tibia with the femur [articulatio femoro-tibialis]: in this joint, by the great providence of Nature, cartilages of this kind specially enhance the depressions in which the heads of the femur are received. In fact, cartilages of this kind do not seem to have been noticed by Galen, save only those [meniscus lateralis, meniscus medialis] which we have said belong to the knee: he mentions them once 9 as ligaments, and only in passing. That they were better known to the Arabs 10 can be inferred because in explaining the structure of the bones they wrote that all bones are connected, the only exception being those in which the Laguahic (or more properly Luhach) intercede and separate the bones somewhat from each other, understanding by the term a cartilage of this kind that in its softness differs little from a ligament. But where these cartilages are located, I have so far found none of the Arabs to explain. 11 This is the role that cartilage plays in the joints.

Cartilage as a glue
Its usefulness comes up again in most junctures of bones not set up for mobility, where cartilage [c. fibrosa] intervenes as if in place of glue, as for example we have noticed happen in joining the bones of the pubis [symphysis pubica] and, in younger bodies, in the joining of an epiphysis with the remaining bone [c. epiphysialis]. There will be occasion to deal further with the nature of attaching cartilage when we discuss the ways in which bones are joined, and it will be necessary to assess it at length in connection with dislocations.

Cartilage in the substance of ligaments
Similarly, the type of cartilage which we will explain sometimes forms cartilaginous ligament will be dealt with in the section on ligaments. Cartilages of this type occur in the connection of the vertebrae, in the hip joint, and in the knee.

Erectile cartilages
For the present it will suffice simply to explain the nature of cartilage in this way. It will not be inappropriate also to mention cartilages made so that anything in them needing to be constantly erect is strengthened. Of this kind are the cartilages [c. fibrosa] of the eyelids, called ta/rsoi [tarsus superior et inferior], 12 which hold up the cilia or hairs of the eyelids that do not fall over like other hairs; 13 such cartilages are like the hard, dry soil in which trees are more firmly set like the oars in long ships when we see them raised out of the water and held stiffly in rows when the ships are not under way.

Cartilages attached to parts that stand erect
Moreover, the Maker of things enhanced with cartilage [c. hyalina] bare and projecting parts of the body as well as the ends of bones not attached to another bone, no doubt so that they should consist of a material too soft to be broken and too dry to be burst. That cartilage no less than finger- and toenails is fashioned from such a material, we learn even from children, who when they get a good-sized cartilage of a cartilaginous fish 14 or a calf, carve it into a little ball and throw it against a rock to make it bounce very high and many times. This resilience plainly argues the mixed character of cartilage, as when one attempts to cut or puncture its surface with a knife and it bounces back. Among the cartilages that border on exposed portions you will observe the cartilages of the nose, the one that comes to a point like a sword [processus xiphoideus] from the end of the sternum, the cartilages of the false ribs, and the one attached to the end of the coccyx [cornu coccygeum]; also the cartilage of the ear [c. elastica], which is thin and supple and covered by the skin, and handsomely supports the body of the ear in place of bone.

Varieties of cartilage
Various additional uses of cartilage explain also their types, so it is unnecessary to explain types or shapes at length, particularly since individual cartilages, like the bones, will come up for separate description. But perhaps one would like it added here that in bodies of a lesser age

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the cartilages are soft; they subsequently harden with age, so that they resemble breakable and friable bone. 15 This happens particularly to the cartilages of the larynx and those which the upper ribs put out. 16 Over time, particularly in animals, these become bony, wrapped only on the outside by cartilage as if by a membrane [perichondrium] which easily separates and is peeled back from the bony substance of the cartilage through boiling.

Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them]