1 64 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 252. — The diaphragm and the muscles of the posterior abdominal wall. 



The anterior abdominal wall and the abdominal viscera have been removed; the thorax has been bent backward 

 so that the lumbar vertebrae are strongly convex forward. 



ligament, the lacunar ligament (Gimbernat' 's ligament) (Figs. 212 and 213), which is also con- 

 nected with radiating fibers of the fascia of the thigh (see page 231). The reflected inguinal 

 ligament (triangular ligament) (Fig. 245) is also formed by radiating fibers from the inguinal 

 ligament, which pass to the posterior surface of the anterior layer of the sheath of the rectus (see 

 page 159). The inguinal ligament gives origin not only to the flat abdominal muscles, but it also 

 furnishes attachment to the fasciae of the abdomen and thigh (see page 231), and the deeper 

 layers of the integument are also adherent to it. 



[The ventral portions of the trunk myotomes during their development undergo a considerable amount of differ- 

 entiation, forming a number of muscle groups. From each myotome a portion is cut off which comes to lie ventral to 

 the vertebrae or ribs, forming what is termed the hyposkeletal group of muscles. Similarly the ventral edges of the myo- 

 tomes are separated to form band-like muscles, whose fibers are directed longitudinally and which are situated immediately 

 adjacent to the mid-ventral line. These constitute what is termed the rectus group. And, finally, the intervening portions 

 of the myotomes divide tangentially into three layers, whose fibers assume an oblique or transverse direction and which 

 constitute what is known as the oblique group of muscles. 



The abdominal muscles are referable to these groups as follows: 



Hyposkeletal: Psoas major and psoas minor (see p. 210). 



Rectus: Rectus abdominis and pyramidalis. 



Oblique: Obliquus abdominis externus, obliquus abdominis interims, transversus abdominis, and quadratus 

 lumborum. 



It is also probable that the intertransversarii laterales of the lumbar region are properly referable to the oblique 

 group. — Ed.] 



THE DIAPHRAGM. 



The diaphragm (Fig. 252) is a single independent muscle, which, from a topographical 

 standpoint, is best considered with the abdominal muscles. Its shape differs from that of all the 

 other skeletal muscles, in that it is a thin and markedly dome-shaped muscle, which is stretched 

 across the inferior aperture of the thorax in such a way that it is convex toward the thorax and 

 concave toward the abdomen. It consists of a central tendinous portion, the central tendon, and 

 of a peripherial muscular portion. 



The muscular fasciculi of the diaphragm are subdivided according to their origin into three 

 parts, which are designated the sternal portion, the costal portion, and the lumbar portion, and of 

 these the lumbar portion is the strongest and the sternal portion by far the weakest. The fibers 

 of all three portions are inserted into the margins of the central tendon. 



The sternal portion (Figs. 252 and 253) arises from the posterior surface of the xiphoid 

 process and consists of but a few slender fasciculi. 



The costal portion (Figs. 252 and 253) arises by broad fleshy serrations from the inner surface 

 of the six lower costal cartilages and from the eleventh and twelfth ribs, being also attached to the 

 lumbocostal ligament in this situation, interdigitating with the transversus abdominis and with 

 the transversus thoracis, following the curvature of the dome of the diaphragm and passing to the 

 central tendon. The fibers of this portion, although weaker than those of the lumbar portion, 



