1352 THE DUCTLESS GLANDS. 



infrequently they are embedded in the thyreoid gland, internal thymus. Less frequently 

 they are sausage-shaped bodies, 5 '25 mm. in length, lying at the sides of the trachea. 

 Sometimes they are long enough to extend into the thorax, where they come into relation 

 with the main thymus gland. Rarely they migrate into the thorax and develop to form 

 considerable portions of the main thymus gland, which then consists of four development- 

 ally distinct parts. Cervical Thymus Vestiges IV. require to be distinguished from the 

 Accessory Cervical Thymus Glands III., which are sometimes found in close relation to 

 parathyreoids III. (see Thymus Gland, Development). 



(v.) THE ULTIMO-BRANCHIAL BODIES. 



The fifth pharyngeal pouches give rise to a pair of gland rudiments called ultimo- 

 branchial bodies. Their fate is not known it is possible that they may become the 

 strands of parathyreoid-like tissue occasionally present in the lateral lobes of the thyreoid ; 

 more frequently, apparently, they degenerate and leave no vestiges. 



Their chief interest is that, for long, they were erroneously regarded as the rudiments 

 of the lateral lobes of the thyreoid gland. 



3. THE DUCTLESS GLANDS ASSOCIATED WITH THE 

 VASCULAR SYSTEM. 



Two ductless glands of mesodermal origin are associated with the vascular 

 system. They are (i.) the spleen, (ii.) the glomus coccygeum. 



i 



(i.) LIEN. 



The spleen is a soft, highly-elastic, contractile organ of purplish colour, placed 

 in the upper left posterior part of the abdominal cavity, partly in the epigastrium, 

 miinly in the left hypochondrium. It is moulded by the diaphragm, kidney, 

 stomach, and, sometimes, colon. Its dimensions vary widely, but on the average 

 are : length, 12 cm. ; breadth, 7 cm. ; thickness, 4 cm. ; weight, 160 gm. Its shape 

 is modified by the relaxation, distension, and contraction of the neighbouring hollow 

 viscera; its position and the details of its moulding, by the attitude of the 

 individual. 



When the stomach is contracted and the colon distended, the spleen has the 

 form of an irregular tetrahedron ; when the conditions of the hollow viscera are 

 reversed, the form of a segment of an orange. These are the extremes of a series 

 of forms which the spleen presents when hardened in situ. In the recumbent 

 posture the long axis of the spleen corresponds in direction with the posterior part 

 of the tenth rib ; in the erect attitude the long axis is frequently vertical, more 

 especially in adult females. 



Surfaces, Borders, and Angles of the Spleen. The surfaces of the spleen are 

 the facies diaphragmatica, facies renalis, facies gastrica, and, in the tetrahedral form only, 

 facies basalis (colica). Their contour is fairly constant. The diaphragmatic surface is 

 convex, moulded to the curve of the diaphragm ; the renal is slightly concave, moulded 

 to the kidney ; the basal is flat or slightly concave, moulded by the colon ; the gastric, 

 deeply concave, moulded by the stomach. The gastric surface is interrupted by an 

 irregular, not infrequently divided, slit, the hilum, through which the branches of the 

 splenic artery enter and the tributaries of the splenic vein leave the gland. On the same 

 surface, behind the hilum, there is a depression for the tail of the pancreas. 



The borders of the spleen are margo anterior, between the gastric and diaphragmatic 

 surfaces ; margo posterior, between the diaphragmatic and renal surfaces ; margo inter- 

 medius, between the renal and gastric surfaces. When present the basal surface is 

 separated from the diaphragmatic by the margo inferior, from the gastric and renal by 

 the margines intermedii, anterior and posterior. 



The anterior border of the spleen is almost invariably notched ; most frequently there 

 are two notches, but there may be six or seven. Sometimes the posterior border also is 

 notched. Rarely, the notches on the borders are joined by fissures extending across the 

 diaphragmatic surface. 



The angles of a tetrahedral spleen are : superior, at the junction of the diaphragmatic, 



