THE BACK 1403 



posterior aspect of the belly wall. In older infants these fibres lose their elasticity, become 

 more tendinous, and then shrink more and more. As they contract they divide, as by a liga- 

 ture, the vessels passing through the ring, thus accounting for the fact that the cord, wher- 

 ever divided, drops off at the same spot and without bleeding. 



(2) Changes in the vessels themselves. — When blood ceases to traverse these, their lumen 

 contains clots, their muscular tissue wastes, while the connective tissue of their outer coat 

 hypertrophies and thickens. Thus, the umbilical vessels and the umbilical ring are, alike, 

 converted into scar tissue, which blends together. This remains weak for some time, and may 

 be distended by a hernia (infantile). 



Finally, we have to consider the state of the umbilicus in adult life. The very dense, 

 unyielding, fibrous knot shows two sets of fibres: — (1) Those decussating in the middle line; 

 and (2) two sets of circular fibrous bundles which interlace at the lateral boundaries of the 

 ring. The lower part of the ring is stronger than the upper. In other words, umbilical hernia 

 of adult life, when it comes through the ring itself and not at the side, always comes through 

 the upper part. In the lower three-fourths of the umbihcus the umbiHcal arteries and m-achus 

 are firmly closed by matting in a firm knot of scar tissue; in the upper there is only the umbil- 

 ical vein and weaker scar. To the lower part run up the umbilical arteries and the urachus. 

 Owing to the rapid growth of the abdominal wall and pelvis before puberty, and the fact 

 that the urachus and the umbilical arteries, being of scar tissue, elongate with difficulty, the 

 latter parts depress the umbilicus by reason of their intimate connection with its lower half. 



Owing to the usual exit of an umbilical hernia of adult life being through the upper part of 

 the ring, the constricting edge in strangulation should be sought below and divided downward. 

 As pointed out by Mr. Wood, it is here that the dragging weight of the hernial contents and the 

 weight of the dress tend to produce the chief results of strangulation. An incision here also 

 gives better drainage if required. 



Coverings of an umbilical hernia. — These, more or less matted together, are: — 

 (1) Skin; (2) superficial fascia, which loses its fat over the hernia; (3) prolonga- 

 tion of scar tissue of the umbilicus gradually stretched out; (4) transversalis 

 fascia; (5) extra-peritoneal fatty tissue; (6) peritoneum. If the hernia come 

 through above the umbilicus, or just to one side, the coverings will be much the 

 same; but, instead of the layer from the umbilical scar, there will be one from the 

 linea alba. 



Strangulated umbilical hernia of adult life. — In this, the most fatal of the strangulated 

 hernise ordinarily met with, the following are practical points in the surgical anatomy: — 1. The 

 coverings, including the sac, are always thin, at times so markedly so that the intra-peritoneal 

 contents are practically subcutaneous. 2. The sac is multilocular, and one or more of its cham- 

 bers may Ue very deep. 3. The contents are numerous, viz., omentum, often voluminous and 

 adherent, transverse colon, and later in the history, small intestine. 4. The contents are often 

 adherent to the sac and each other, thus explaining the irreducibility. 5. The long duration 

 of the presence of the transverse colon with its stouter walls accounts for the period, often pro- 

 longed, in which warning evidence of incarceration precedes that of strangulation. 6. The 

 communication with the peritoneal sac is direct, short, and dm-ing a prolonged operation, free. 

 Infection is thus readily brought about. 



THE BACK 



The surface form and landmarks of the back will be considered first, followed 

 by the relations of skeleton, muscles, viscera and nervous sj-stem. 



Median furrow. — This is more or less marked according to the muscular 

 development, lying between the trapezii and semispinales capitis, in the cervical 

 region, and the sacro-spinales lower down. The lower end of the furrow corre- 

 sponds to the interval between the spines of the last lumbar and the first sacral 

 vertebrae. (Holden.) 



Vertebral spines. — Those of the upper cervical region are scarcel}^ to be made 

 out even hj deep pressure. That of the axis may be detected in a thin subject. 

 Over the spines of the middle three cervical vertebrae is normally a hollow, owing 

 to these spines receding from the surface to allow of free extension of the neck. 

 The seventh cervical is prominent, as its name denotes. Between the skull and 

 atlas, or between the atlas and epistropheus, a pointed instrument might pene- 

 trate, especially in flexion of the neck. 



Of the thoracic spines, the fu-st is the most prominent, more marked than that of the last 

 cervical; the third should be noted as on a level with the medial end of the scapular spine, and 

 in some cases with the bifurcation of the trachea; that of the seventh with the lower angle of 

 the scapula; that of the twelfth with the lowest part of the trapezius and the head of the twelfth 

 rib. The obliquity and overlapping of the thoracic spines are to be remembered. 



Of the lumbar spines, the most important are the second, which corresponds to the termi- 

 nation of the cord, and the foiuth, which marks the highest part of the iliac crests and the 

 bifurcation of the abdominal aorta. The lumbar spines project horizontally, and correspond 

 with the vertebral bodies. The third is a Uttle above the umbilicus. 



