FASCIA 425 



ternal oblique and the cremaster muscle, below by the reflected portion of the in- 

 guinal ligament, dorsally by the transversalis fascia and above by the transversus, 

 internal oblique, and cremaster muscles. 



The quadratus lumborum (fig. 406), which extends from the twelfth rib to the' 

 ilium and ilio-lumbar ligament, is supplied by direct branches of the lumbar nerves^ 

 in series with the nerves supplying the musculature of the abdominal wall. It 

 will, therefore, be taken up with the intrinsic thoraco-abdominal muscles. It 

 depresses the thorax and abducts and extends the spine. The psoas muscle, on 

 on the other hand, which also hes at the back of the abdominal cavity, represents 

 an extension of the intrinsic musculature of the limb to the spinal column (see/ 

 p. 455). ^ 



The diaphragm (fig. 391), a dome-shaped muscle which is attached to the distal 

 margin of the thorax and to the upper lumbar vertebrae, and separates the thoracic 

 and abdominal cavities, arises in the embrvo in the region of the neck, and main- 

 tains cervical relations through its innervation by the phrenic nerves, which spring 

 one on each side usually from the third to fifth cervical nerves. It does not belong 

 morphologically with the other muscles considered in this section, but is here 

 included because of its physiological and anatomical relations and the convenience 

 of treating it in connection with the intrinsic thoraco-abdominal muscles. A 

 diaphragm completely separating the thoracic from the abdominal cavities is 

 found only in the mammals. The central portion of the diaphragm is an aponeu- 

 rosis or central tendon with a convex ventral and concave dorsal margin. Into 

 this tendon is inserted the musculature which arises on each side from the xiphoid 

 cartilage, the cartilages and tips of the last six or seven ribs and by means of three 

 crura from the sides of the first four lumbar vertebra?. 



In fishes and tailed amphibians the musculature of the body wall is composed of meta- 

 merically segmented musculature. In all higher vertebrates it is hkewise at an early embrj^onic 

 stage segmental, being composed of the ventro-lateral portions of the myotomes. The ventral 

 ends of the myotomes give rise to a ventral longitudinal muscle which runs on each .side of the 

 body next the mid-hne in front, and retains more or less of the primitive segmentation. The 

 rectus abdominis and the infrahyoid muscles represent this system in man. Very frequently 

 traces of the system may also be seen on the upper thoracic wall in the form of slender muscular 

 and aponeurotic slips. The rectus muscle in man is usually developed from the last seven tho- 

 racic myotomes. The pyramidalis becomes spht off from its lower end. The lateral part of 

 the ventro-lateral portions of the thoracic myotomes usually gives rise to several strata of mus- 

 cles which vary somewhat in different vertebrates, although quite similar among the mammals. 

 In man the twelve thoracic and first two lumbar myotomes give rise to the lateral musculature 

 of the thoraco-abdominal wall. 



The quadratus lumborum represents the ventro-lateral portions of the lumbar myotomes 

 with the exception of that portion of the first two which enter into the lateral abdominal mus- 

 culature and of the fifth, which probably undergoes retrograde metamorphosis. 



It will be noted that the abdominal wall is composed of musculature which has an origin 

 chiefly from the thoracic myotomes. At an early stage of embryonic development both the 

 thoracic and the abdominal viscera are covered by a non-muscular membrane. The myotomes 

 extend into this from the thoracic region, and as tbe musculature is differentiated, it approa,ches 

 the median hne in front and extends distally to the pelvis. Owing to the rotation of the limbs 

 the abdominal musculature is stretched ventrally over an area corresponding to the lumbar 

 and sacral regions dorsally The last part of the thoraco-abdominal wall to be furnished with 

 musculature is that about the umbihcus. Occasionally the process fails to be completed in this 

 region. 



Each spinal nerve supplies primarily the musculature derived from the myotome which lay 

 caudal to it, and at first the musculature hes wholly superficial to the nerves. With subsequent 

 differentiation the metamerism is somewhat obscured by anastomosis of nerves and fusion of 

 myotomes; and a part of the internal oblique layer and all the transverse layer of the lateral 

 musculature comes to he on the inner side of the main nerve-trunks. 



FASCIiE 



The fasciae and the topographical relations of the thoraco-abdominal muscles may be fol- 

 lowed in the sections shown in figs. 357, 384, and 407. 



Tela subcutanea. — As mentioned above, most of the intrinsic thoracic musculature is cov- 

 ered by other muscles, while the superficial layer of the abdominal musculature is subcutaneous. 

 A panniculus adiposus, Camper's fascia, in which much fat may be deposited is usualh' easily 

 distinguishable, especially in the lower part of the ventral wall of the abdomen, from a membran- 

 ous fascial sheet which is loosely attached to the underlying fascial envelopment of the muscles. 

 To this membrane has been apphed the term Scarpa's fascia. Near the groin it is separated 

 from the panniculus adiposus by blood-vessels and lymphatic glands. It is closely bound to the 

 Unea alba between the two rectus muscles, to the fibrous structures in front of the pubic bone, 

 to the fascia lata below the inguinal Hgament, and to the crest of the ihum. 



Over the scrotum of the male and vulva of the female both layers of the tela subcutanea are 

 continued. In the male the fat of the more superficial layer disappears and the two layers 



/ o « 



