6 Anatomy of Skeleton 



structures, and to think of its different parts in terms of these as they exist in the 

 living body. 



2. In addition to the secondary mouldings just mentioned there are secondary 

 markings to be distinguished on bones. These are made by ossification spreading a 

 little way into the attachment of fibrous tissue to the periosteum, and become evident 

 after birth, as a rule about puberty. They indicate fibrous attachment only, be it liga- 

 ment, tendon, aponeurosis, or fascia, and are never made as a result of attachment 

 of purely muscular fibre. They are manifestly surface elevations or markings and 

 easily distinguished from primary ridges in the bone. An excellent example is seen 

 in the oblique or vertical line on the tibia or the deltoid impression on the humerus. 

 Sometimes the secondary marking is placed on a primary ridge, as in the linea aspera 

 of the femur : at birth there is only the primary posterior border visible on the shaft, 

 into which the aponeuroses are inserted, but later the bony growth invades these 

 fibrous structures and thus the secondary linea aspera is added to the primary posterior 

 border. Secondary markings are not always so apparent, and in some cases may 

 be hardly visible, but they can always be felt by the finger, and it is a good 

 thing for the student to acquire the habit of examining all bony surfaces with the 

 finger, which, with a little training, will be found more useful than the eye for 

 certain purposes. 



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 



