136 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



which dips down between them is part of the deep fascia. It forms a sheath, the 

 perimysium, for each fasciculus. The part of the muscle which is composed of 

 fasciculi with their perimysia, is known as the fleshy part of the muscle, or the 

 belly. The fasciculi do not extend completely to the ends of a muscle, but the 

 deep fascia does. Consequently the ends of muscles are non-fleshy, composed 

 of connective tissue only. These connective tissue ends of muscles commonly 

 form tough shining bands or cords, known as tendons. When the tendon is very 

 broad and flat, it is often called an aponeurosis, or the name fascia may be retained 

 for such broad tendons. The attachments of muscles are always by means of 

 tendons, aponeuroses or fasciae, never by the muscle fibers. Muscles are 

 attached to bones or to tendons, aponeuroses, or fasciae, which themselves 

 are attached to bones. The purpose of the voluntary muscles is to move the 

 bones of the skeleton. 



The anterior part of the external oblique is concealed under a large flat 

 muscle, the latissimus dorsi, which covers the anterior part of the back and slopes 

 toward the upper arm. The posterior boundary of this muscle should be located 

 and slit, and it should then be lifted from the surface of the external oblique by 

 thrusting the fingers between. If fat is present between these two muscles, it 

 must be cleaned away. The most posterior chest muscles also cover the anterior 

 part of the external oblique and should be lifted off in a similar manner. The 

 external oblique will then be found to be attached to the posterior ribs by separate 

 slips. The fixed points of attachment of a muscle are called its origin. When 

 there is more than one origin, each one is known as a head. When there are 

 a number of points of attachments segmentally arranged, they are generally 

 designated as slips. The origin of the external oblique is from the posterior 

 ribs by separate slips and from the lumbodorsal fascia. Its fibers (fasciculi) 

 pass obliquely downward and backward, and in the rabbit the more dorsal 

 ones pass nearly straight caudad. The movable points of attachment of a 

 muscle on which it exerts its effect are called its insertion. The insertion of the 

 external oblique is by way of an extensive aponeurosis which passes to the 

 median ventral line. The insertion is: rabbit, on the linea alba by its aponeu- 

 rosis and on the inguinal ligament, which is in turn attached to the ilium and the 

 pubic symphysis; cat, on the linea alba and the pubis by its aponeuroses, and 

 on the median ventral line (raphe) of the thorax. The function of a muscle 

 is called its action. The action of the external oblique is constrictor of the 

 abdomen. 



In the following dissection of the muscles the dissection is to be confined 

 strictly to the left side, leaving the right side intact for the dissection of other 

 systems. 



3. The muscles of the abdominal wall. — The abdominal wall is composed 

 of three layers of muscles with their aponeuroses. The aponeuroses of these 

 muscles are quite extensive. The three layers are: an external layer, the 



