STRUCTURE OF THE MUSCLES 283 



attachment, it is very necessary to bear in mind not only those to bone and 

 curtilage, but also those to the til)roiis septa and aponeuroses which lie between 

 and around the muscles. Such attachments are best seen when the area of 

 bone surface available for origin or insertion is small. By this means a very 

 great extension is given to this area, and a small bony process, such as the inner 

 condyle of the humerus, is able to give a firm resistance to the traction of many 

 strong muscles. 



4. The structure will include not only the direction and cur\'-ature of the fleshy 

 fibres, and the extent of fibrous tissue by which these fibres arise or are inserted ; 

 but also the internal arrangement of tendons and muscular fibre, which is often 

 of a somewhat complicated character. The simplest structure of all is that of 

 muscles with no tendons, in which the fleshy fibres run parallel from one end to 

 the other. Many of the small muscles of the face are of this character. The 

 sterno-mastoid and sartorius are examples also of muscles in which the parallel 

 fleshy fibres form nearly the whole of the structure. It will be found that in these 

 muscles, on account of the number of joints passed over and the distance of the line 

 of the muscle from the axes of these joints, the range of movement is very great. 

 In most parts of the body, however, there would be a great waste of fleshy fibre if 

 this arrangement prevailed. Roughly speaking, we may say, that when fleshy 

 fibres contract fully, their length is diminished by one half. Now, if the distance 

 l)etween the movable points of the skeleton which are joined by the muscles can- 

 not l)e lessened by this amount, it is obvious that some of the contractile power 

 of the muscle would be wasted. When, therefore, the movable points of the 

 skeleton bridged by a muscle can only be approximated through a limited space, 

 it will be found that the parallel fleshy bundles are about twice the length of this 

 space, and that the rest of the muscle consists of inextensible tendon, which acts 

 simply as a ligament to attach the contractile muscle to the bones. But this 

 addition of tendon to the fleshy part of the muscle is effected in various ways. The 

 simplest plan is that in which the addition is made at one end or the other of the 

 muscle. The palmaris longus is to some extent an example of such an arrange- 

 ment. By examining the bones it will be seen that the front of the carpus cannot 

 be approximated to the internal condyle of the humerus by more than three inches. 

 The fleshy bundles are, therefore, of about twice this length, and they are accumu- 

 lated towards the upper end of the muscle, while the rest of its length is occupied 

 by a long tendon. A more common arrangement is for the short fleshy fibres to 

 arise in succession along the surface of a long bone or from an intermuscular 

 septum, and to pass in parallel lines to the end and side of a long tendon, which 

 gradually thickens with the increase of the number of the fibres inserted into it. 

 Such a muscle is like a feather, of which the quill with its diminishing upper 

 extremity Avill represent the tendon, and the barbs upon one side of it the fleshy 

 fibres. Hence this arrangement is called penniform, from penna, a feather (fig. 

 259). This form is found when consideral)le power is required, but with only a 

 small range of movement. To appreciate fully the effect of such a muscle, Ave 

 should in our imagination take all the short parallel fibres and place them side by 

 side at the end of the tendon. The muscle would then be converted into a very 

 thick and short fleshy mass with a very long tendon. 



Frequently a muscle arises in two lines from the adjacent surfaces of two bones, 

 from which two sets of parallel fibres converge upon a tendon which runs down in 

 the interval between the bones. This arrangement resembles a feather with barbs 

 on either side of the quill, and is called hipenniform. Examples of both these 

 forms are found in the leg. The peronei arising from the fibula alone are penni- 

 form, while the til)ialis posticus and soleus, arising from l)oth tibia and fibula, are 

 bipenniform. 



In some cases a further complication is introduced by the origin of a muscle 

 from both sides of several fibrous septa, as well as from the intermediate surfaces 

 of the bone to which the septa are attached. The insertion may also be of the same 

 character. A good example of this, which is called the mu hi penniform arrange- 

 ment, is the deltoid, a very powerful muscle with a short range of movement. 



In some few cases the tendon is intercalated between two fleshy masses. Such 

 muscles are called biventral. The central tendon may represent a bony structure 



