UMBILICAL HEENIA. 397 



opening. At the same time the vessels become obliterated and 

 themselves converted into a mass of scar-tissue, at first weak, 

 but later of considerable denseness and firmness. 



In adult life the umbilicus shows two sets of fibres about it, 

 one decussating across the middle line, and the other of circular 

 direction around the aperture or pseudo-aperture itself. These 

 form the so-called ring, which is stronger at its lower than at 

 its upper part. The scar-tissue in the upper margin of the 

 opening is less firm than in the lower, owing to the fact that in 

 the former region there are only the remains of the umbilical 

 vein, while in the latter are found the obliterated urachus and 

 the arteries. 



If the two halves of the abdominal wall fail to unite in any 

 marked degree in the region of the umbilicus, a true " congenital " 

 umbilical hernia will result. 



Dilatation of the scar-tissue at the umbilicus after the fall of 

 the cord constitutes an acquired umbilical hernia. " infantile " 

 when in a young subject, " adult " after infancy. 



The tissues covering an acquired umbilical hernia become 

 rapidly stretched, and there is a tendency for the peritoneum 

 forming the sac to become fenestrated. The contents of such a 

 hernia are often irreducible owing to adhesions, partly within 

 the sac, but partly, also, to the external tissues, if the sac is 

 fenestrated. 



DISEASES OF THE SALIVARY GLANDS. 



Wounds of the Parotid Region. The parotid gland contains 

 within its substance very important structures. The formation 

 of the temporo-maxillary vein in the upper part of the gland 

 by the union of the superficial temporal and internal maxillary 

 veins, and its course somewhat superficially downwards through 

 the gland, renders this venous trunk particularly liable to injury 

 in punctured \vounds of this region. Deeper than the vein 

 lies the external carotid artery breaking up into its terminal 

 branches, the superficial temporal and the internal maxillary. 

 It again may be damaged but much more rarely. Deepest of all 



