72 THE VOYAGE OF H.M.S. CHALLENGER, 



posterior fibres are inserted into the integument immediately behind the anus, and the 

 intermediate fibres are inserted into the aponeurosis of the abdominal muscles, close to 

 the lateral margin of the anus. 



Action. — This muscle, acting in conjunction with its fellow of the opposite side, will 

 diminish the size of the abdominal cavity, by elevating and approximating the abdominal 

 wall to the vertebral column. As remarked by Gervais and Alix, it also acts as a 

 superficial levator ani. 



Relations. — This muscle at its origin lies between and separates that of the levator 

 coccygis from that of the semi-tendinosus. As it passes downwards to its insertion it 

 rests against the ischio-pubo-coccygeus. 



Nerve siq^ply- — -Several twigs from the anterior divisions of the coccygeal nerves. 



2. Obliquus abdominis externus. 



Le grand oUique, Vicq d'Azyr, 1774, p. 490, No. 1. 

 Aeiisserer schrager Bauelimuskel, Merrem. 

 Der dussere schiefe Bauchmuslcel, Wiedemann, p. 79. 

 Der dussere schrdge Bauchmuskel, Tiedemann, p. 296, No. \. 

 Grand oblique, Cuvier, vol. i. p. 217. 



Muscle oblique exteme de Vabdomen, Meckel, vol. vi. p. 18, Xo. 1. 

 Obliquus abdominis externus, Selenka, vol. vi. p. 102, No. 25. 

 Obliquus abdominis externus, Owen, p. 30. 

 Le grand oblique, Gervais and Alix, p. 17. 



Attachments. — The external oblique is a broad flat muscle, which arises by means of 

 seven digitations from the outer surfaces of the vertebral segments of the last seven 

 ribs, and by means of a delicate aponeurosis fi'om the whole length of the lower border 

 of the pubic bone. Each costal digitation is attached to the rib immediately below 

 the uncinate process, and to a small extent to that process itself. From this extensive 

 origin the muscular fibres pass obliquely backwards and downwards, and are inserted 

 as follows. The anterior or costal fibres of the muscle are inserted into the lateral 

 margin of the sternum from the facet for the reception of the third sternal rib backwards 

 to the posterior extremity of the bone, while the posterior or pubic fibres end on a 

 stout aponeurosis which completes the abdominal wall. 



Action. — As observed by Tiedemann, this muscle aids in respiration by approximating 

 the sternum to the vertebral column, and diminishing the capacity of the thoracic and 

 abdominal cavities. 



Relations. — The muscle interdigitates with the serrati antici major et minor. 

 Superficially it is in part concealed by the aponeurotic origin of the semi-membranosus, 

 while its deeper surface rests upon and conceals the ribs and intercostal muscles in front, 

 and the rectus abdominis behind. 



Nerve supply. — Twigs from the intercostal nerves. 



