MUSCLES OF THE TRUNK. 305 



woven into each other. The small oblique covers the rectus and transversalis 

 abdominis. 



Action. — This muscle, a congener of the preceding, compresses the abdominal 

 viscera, depresses the last ribs, and causes the flexion — either direct or lateral — of 

 the vertebral column. 



The retractor muscle of the last rib. — This small muscle, flattened on each side 

 and triangular in form, originates by aponeurotic fibres from the summits of the 

 first two or three transverse processes of the lumbar region. It terminates on 

 the posterior border of the last rib. Covered by the last digitation of the 

 posterior serratus and by the great oblique, it covers in turn the transversalis 

 abdominis. In contracting, it draws the last rib backwards, and fixes it in that 

 position, in order to permit the expiratory action of the internal intercostal 

 muscles. It therefore plays the same part, in regard to these muscles, that the 

 scalenus does to the external intercostal muscles (Fig. 162, 17). 



5. Geeat Straight Muscle of the Abdomen (Rectus Abdominis) 

 (Figs. 162, 20 ; 176, 9). 



Synonym. — Stemo-pubialia — Girard. 



Situation — Extent — Form — Stricture. — This is a wide and powerful muscular 

 band, extending from the sternum to the pubis, included between the aponeurosis 

 of the internal oblique and that of the transversalis muscles, narrower at its 

 extremities than in its middle, and divided by numerous transverse and zig-zag 

 fibrous intersections. These strongly adhere to the aponeurosis of the small 

 oblique muscle, are nearer to each other, and more distinct, in front than behind, 

 and are produced by small tendons which are placed at certain distances on the 

 course of the muscular fasciculi, making it somewhat of a polygastric muscle. 



Attachments. — In front : 1. To the prolonging cartilages of the last four 

 sternal and the first asternal ribs. 2. To the inferior face of the sternum. 

 Outwardly, by the anterior moiety of its external border, to the internal face of 

 the great oblique. Behind, to the anterior border of the pubis, through the 

 medium of the common tendon, which is a direct continuation of the rectus 

 abdominis. 



Relations. — By its inferior face, and in front, with the pectoralis magnus and 

 great oblique ; for the remainder of its extent, with the aponeurosis of the small 

 oblique. By its superior face, with the transversalis muscle and the cartilages of 

 several ribs. By its internal border, with the white hue, which separates it from 

 the opposite muscle. 



Action. — It draws the thorax backwards, and compresses the abdominal 

 viscera. It is also the principal flexor of the spine. (Leyh, remarking that 

 it shares in the functions of the preceding muscles, adds that it draws the pelvis 

 forwards during copulation.) 



6. Transverse Muscle of the Abdomen (Transversalis Abdominis) 

 (Figs. 163, 18 ; 176, 12, 12). 



Synonyms. — Lumbo-abdominalis — Girard. (The costo-abdoniinalis internus of Leyh.) 



Sittmtion — Composition. — This muscle is situated immediately outside the 

 peritoneum, and forms the deep layer of the abdominal parietes. It is musculai 

 outwardly, and aponeurotic for the remainder of its extent. 



