240 THE MUSCLES. 



separated from the fleshy portion. It is traversed by several openings which 

 afford passage to the subcutaneous vessels and nerves of the abdominal 

 region. 



The abdominal tunic acts as an immense elastic girth or bandage, which 

 aids the muscles in sustaining the weight of the intestines. As the digestive 

 organs increase in volume this tunic increases in thickness. 



In the Pig, Dog, and Cat, it is reduced to a simple cellulo-aponetirotic lamina, owing 

 to the stomach and intestines in these animals exercising but a small amount of prtssure 

 on the abdominal parietes. 



2. White Line. 



The white line (linea alba) is a fibrous cord comprised between the 

 internal border of the two great straight muscles, and is considered as being 

 formed by the intercrossing, on the median-line, of the aponetiroses belonging 

 to the oblique and transverse muscles. Attached, in front, to the inferior 

 surface of the xiphoid appendage, this cord is confounded, behind, with a 

 large tendon, the prepubic or common tendon of the abdominal muscles, which 

 is fixed to the anterior border of the pubes (Figs. 90, A ; 108, c; 116, 4). 

 This tendon, covered by the abdominal tunic, contributes to form the 

 internal commissure of the inguinal ring, and gives origin to the pubio-femoral 

 ligament. 



Towards the union of its posterior third with its two anterior thirds, 

 the white line widens, so as to form a lozenge-shaped space, in the centre 

 of which is found the remains of the umbilicus and thu umbilical cord 

 (Fig. 116, 14). 



3. Great Oblique, or External Oblique of the Abdomen. (Figs. 105, 18 ; 116, 5.) 

 Synonyms. Costo-abdominalis Girard. (Obliquus externus dbdominis Percivall.) 



Situation Composition. This muscle, the largest and the most super- 

 ficial of the four, is composed of a fleshy and an aponeurotic portion. 



Form, Structure and Attachments of the fleshy portion. This is composed 

 of fibres directed obliquely downwards and backwards, and presents itself as 

 a wide muscular band, narrower before than behind, applied to the inferior 

 surface of the last thirteen or fourteen ribs. Its superior border is concave, 

 and attached : 1, To the external surface of the ribs just mentioned by as 

 many slightly aponeurotic digitations, the first four of which cross the denta- 

 tions of the great serratus ; 2, To the aponeurosis of the great dorsal muscle, 

 from the last rib to the external angle of the ilium (Fig. 105, 18). Its inferior 

 border, convex and sinuous, is continuous with the aponeurosis ; it descends, 

 in front, to the cartilaginous circle of the false ribs, which it projects beyond 

 posteriorly, increasing in this as it nears the lumbar region. 



Form, Structure, and Attachments of the aponeurosis. This is narrow and 

 thin in front, wide and thick behind, of a triangular form, and composed 

 of white, nacrous-looking fibres passing in the same direction as the fibres 

 of the fleshy portion, with whose inferior border it is continuous by its 

 external border. Its internal border is inserted into the white line and the 

 prepubic tendon ; and its posterior border, extending from the external 

 angle of the ilium to the anterior border of the pubis, responds to the 

 plicature of the flank, embraces the corresponding crural muscles, and 

 establishes the line of demarcation between the trunk and the abdominal 

 limb (Fig. 116, 10). 



The aponeurosis of the great oblique gives rise, at its posterior border, 

 to two very remarkable fibrous leaves which appear to be produced by the 



