Pressure and saving of space are at the bottom of tendon-formation, and thus in the body, where the mass of the packed muscles exceeds that of the skeleton, the muscles narrow to their attachments on the bones as a rule, i.e., they have their muscle fibres ending partly or altogether in less bulky tendons : this is particularly noticeable where they pass over joints, to allow for movement without compression of other structures. Thus it comes about that secondary markings are present to indicate the attachments of most of the muscles, but the marking is only for the fibrous tissue, and therefore may not by any means correspond with the whole area taken up by the actual attachment. A purely muscular insertion must have practically the same area as the section of the muscle, whereas a tendon can thin down to a very small size, whence we reach the conclusion that the amount of secondary marking for any muscle will be inversely as the amount of pure muscle reaching the bone, or, in other words, caeteris paribus, the larger the area the smaller the amount of secondary marking in general. Used with knowledge and proper care these markings are of the utmost value in obtaining an accurate notion of attachments and consequently of relations of a bone, and the understanding eye can learn from them other facts about other structures : for instance, we know without further investigation that Tibialis posticus has one or two intramuscular tendons, from the fact that its area of fibular origin is crossed by one or two secondary "oblique lines," or the absence of a secondary capsular marking on the back of the neck of the femur might lead us to infer that there are no transverse fibres on the back of the capsule and presumably therefore only circular fibres.
But although muscles make no secondary markings, yet their areas of attachment can occasionally be made out by a careful and close inspection, revealing in a fine bone a slight change in what might be called the " surface texture " of the bone : this, however, is not a secondary marking in the sense used above. It is better to confine the use of the term to a spread of ossifying process and thus not to include such changes or the impressions produced by nerves or vessels, etc., in contact with the bone.
We might sum up this part of the subject by saying that the student should study the groups of muscles and other structures that lie against the bone and thus see how the different surfaces come into being, that he should see how these surfaces may have shape and level altered by the primary " build " of the bone, and should notice the secondary markings on the surfaces, remembering that they indicate fibrous attachment, and making use of them to mark out the accurate and detailed relations of the various aspects of the bone.
The key to many things that puzzle the student of anatomy is to be found in a study of the bones of a part, and it should be a rule for every dissector that he must undertake his dissection of a part with the skeleton of the region beside him, so that he may constantly refer from one to the other and back again ; in this way he will begin to understand how and why certain structures are found in certain situations, and to look at them from new points of view. It is a common error to imagine that any explanation of some anatomical fact or relation can only be sought in its development-it will repay the student to seek for mere mechanical and physical reasons for what he observes, for these can be brought in directly in all sorts and conditions of anatomical matters : then, if he wishes to pursue the subject further, he will have a -point d'appui from which to direct his embryological or other researches. He should bear in mind that the disposition of the soft parts has its effect on the structure of the bones, and he should look for this as much as for the effect that the bones produce in the arrangement of the tissues. In this way he will obtain an idea of the skeleton as it exists in the body, with all its attachments and relations-a much more interesting study than that of the dry bones lying on the table, and one that will be of everyday use to him in future practice.
To study the skeleton, however, it is necessary to use the dry bones, but if the student makes a point of trying to find reasons for the various things he observes on the specimen, he will not only add to the interest of his occupation but will be surprised to find how much descriptive anatomy can be appreciated from such a study.
When considering bones or reading descriptions of them-such, for example, as are given in this book-the student should take care to have the specimen before him ; a description that is not verified is of little permanent value, and the reader ought to make a point of referring every statement made in the description to the test of observation on the specimen. For this reason he should be provided with several examples of the particular part of the skeleton he is studying, for comparison between many specimens is the best way of impressing the main or fundamental points of any structure on the mind, in spite of individual variations. Also he ought, whenever it is possible, to have the various appropriate dissections and preparations that enable him to appreciate the bones in situ, and constant reference to these will be of the utmost benefit. Finally, he should always see how much of the skeleton can be felt and studied on his own or some other living body.
The particular bone that he studies, and with which the other specimens are compared, should if possible be one from an adult male in which the secondary markings are well developed, but not excessively so.
In the account of the skeleton that follows each bone is at first described shortly, and a reader approaching such a study for the first time ought to go carefully through the description with the bones beside him, until he is acquainted with the general build and form of the particular bone and the names, position, and nature of all its principal parts, for he is not able to understand further details until he has mastered these elementary matters.
A longer consideration of things concerning the bone follows. Such a consideration could not be understood unless the reader had dissected the part concerned, so it is assumed, that he has done so and is more or less familiar with it. It is in this part particularly of the description that the bones for comparison and the dissections ought to be used for constant reference, and it must not be forgotten that the descriptions are intended for application to the specimens and not to the drawings : the majority of figures in the following pages are introduced as guides to facilitate the recognition of the various parts on the actual skeleton. There can be no other object in having drawings of bones, and Anatomy cannot be learnt from pictures.