528 HUMAN ANATOMY. 



emaciation the whole anterior abdominal wall becomes concave (scaphoid), especially 

 the upper portion bounded by the ensiform cartilage and the subcostal angle, — the 

 scrobiculus cordis (page 171), — which, with the patient supine, may appear to rest 

 directly upon the vertebral column, with walls more nearly vertical than horizontal. 



Congenital deforinities of the abdominal wall usually consist in a failure of the 

 ventral plates to unite in the middle line, producing various degrees of umbilical 

 hernia {q-v.) or leaving the contents of the abdomen uncovered over a considerable 

 area. 



Contusions of the anterior abdominal wall, bounded laterally by the outer free 

 border of the external oblique, — i.e., by a line just external to a vertical line dropped 

 from the lowest part of the ninth rib, — are of importance in relation to the eflect 

 upon the organs contained within the abdomen. As the skin over the abdomen and 

 the abdominal muscles receive their nerve-supply from the lowest six intercostal 

 nerves and the branches of the anterior division of the first lumbar, the contraction 

 of the muscles upon the approach of danger, if not voluntary, may be reflexly 

 hastened at the moment of external application of force, and a pFotecting elastic 

 barrier may thus be interposed between the latt^ and the abdominal contents. The 

 rigidity caused by the contact of a cold hand with the abdominal surface, preventing 

 palpation of the viscera beneath, affords a familiar illustration of the close relation 

 between skin and muscles. The relation of the nerve-supply of the muscles and 

 that of the underlying viscera explains the rigidity of the belly so usually seen in 

 injury or disease of abdominal organs (page 1683). Finally the relation of the cuta- 

 neous and muscular branches of the intercostal nerves is well shown by the sudden 

 inspiratory effort caused by a dash of cold water on the lower thoracic or abdominal 

 region, six of these nerves supplying the intercostal muscles as well as the antero- 

 lateral surface of the chest and belly. 



The injurious effect of contusions is diminished by the presence of a thick layer 

 of subcutaneous fat or by the interposition of a fleshy omentum. If the abdominal 

 muscles are relaxed, serious injury to the viscera may be done without obvious 

 damage to the parietes. Absence of ecchymosis or other visible sign of injury should 

 therefore not lead to an absolutely favorable prognosis until after the lapse of sulifi- 

 cient time to permit of the development of visceral symptoms. 



Wounds. — The thinness and loose attachment of the skin of the abdomen favor 

 the occurrence of cellulitis as a result of infection from superficial wounds. The 

 superficial layer of the superficial fascia contains the greater part of the subcutaneous 

 fat and covers the superficial blood-vessels. The thickness of the abdominal wall 

 depends chiefly upon the thickness of this fatty layer, which may be of several inches. 

 An abdominal wound may therefore be of considerable depth and yet be attended by 

 little or no bleeding and be practically ' ' superficial. ' ' The deeper layer of the super- 

 ficial fascia (page 515) is firmer, is elastic, and in its lower part is the vestige of the 

 "tunica abdominalis," well developed in the horse and some other quadrupeds for 

 reinforcement of the abdominal muscles, on which the weight of the viscera comes 

 more directly than in man. It is attached in the middle line to the deeper struc- 

 tures and to the iliac crest, and below Poupart' s ligament blends with the fascia lata 

 of the thigh. It is not attached over the space between the pubic spine and symphysis, 

 but, being carried downward over the spermatic cord, becomes continuous with the 

 dartos layer of the scrotum and with the fascia of CoUes. Cellulitis superficial to this 

 layer may therefore spread in all directions, but beneath it is likely to be at least tempo- 

 rarily arrested at the lines of attachment indicated. General emphysema, effusions of 

 blood, and collections of pus have for a time similar limitations. They are apt to be 

 guided by this fascia into the space between the spine and the symphysis and to descend 

 into the scrotum and towards the perineum, where the lateral attachments of Colles's 

 fascia to the margins of the pubic arch and posteriorly to the base of the triangular 

 ligament prevent their spreading in those directions. More usually the extravasa- 

 tion — blood, pus, or urine — gains this subfascial space below, as from rupture of the 

 urethra anterior (inferior) to the triangular ligament (page 1932), and ascends to the 

 abdomen by the same route, being prevented from crossing the mid-line or descend- 

 ing to the thighs by the attachments of the deep layer of the superficial fascia that 

 have been described. 



