296 CLINICAL APPLIED ANATOMY. 



mediastinal fascia explains those instances in which inflammation 

 has spread to the gland as a sequel of pleurisy, pericarditis, 

 retropharyngeal and other abscesses in the neck, &c. 



The thymus gland may be the site of epithelial, sarcomatous, 

 lymphatic, fatty or other tumours. In this connection it is 

 interesting to remember that it is developed as an epithelial 

 structure, derived from the dorsal part of the third visceral cleft, 

 represented in the adult by the space in front and on each side 

 of the epiglottis. Later the gland is transformed into lymphoid 

 tissue, whether by local growth or invasion from without is 

 doubtful. Epithelial remnants remain in the form of the 

 concentric corpuscles. The surrounding mesoblast supplies the 

 capsule and the connective tissue stronia of the gland. Hence 

 there are elements from which epithelial, connective tissue, or 

 lymphoid neoplasms may arise. 



THE SPLEEN. 



Injuries of the spleen are not very common. The depth at 

 which the organ lies in the left hypochondriac and adjacent part 

 of the epigastric regions affords it protection. When enlarged 

 the spleen becomes much more superficial anteriorly, and is 

 liable to rupture by direct violence or vigorous muscular contrac- 

 tion. Normally the spleen lies under cover of the ninth, tenth, 

 and eleventh ribs of the left side. Its long axis corresponds with 

 the posterior part of the tenth rib, its posterior extremity lies an 

 inch and a half away from the spinal column, and its anterior 

 border reaches the mid-axillary line. It may be wounded when 

 the ribs under which it lies are fractured and their broken ends 

 driven inwards. Under such circumstances the diaphragm is 

 penetrated, and the left lung and pleural sac, which overlie the 

 spleen, may be damaged. The elasticity of the ribs and the 

 yielding nature of the abdominal wall may allow the spleen to 

 be severely crushed against the spinal column and lacerated 

 without the occurrence of fracture or external bruises. The 

 liver is often lacerated at the same time as the spleen. The 



