PRACTICAL CONSIDERATIONS : THE SPLEEN. 1787 



also a few superficial ones. They empty into a little group of lymph-nodes at the 

 tail of the pancreas. 



The nerves, from the solar plexus, enter the hilum with the vessels. 



Development and Growth. — The splenic anlage appears about the fifth 

 week of foetal life as a slight condensation of the mesoblastic tissue of the meso- 

 gastrium, associated with local thickening of the mesothelium clothing the left surface 

 of this serous fold. According to Tonkof?,^ the mesoblast is invaded by migrating 

 cells from the mesothelium, which play an important role in the production of the 

 pulp-cords, the trabeculae resulting from the differentiation of the vascular mesoblastic 

 tissue. The Malpighian bodies appear relatively late as accumulations of young 

 lymphocytes. 



At birth the spleen weighs from 10-15 S^'^-' ^^^ is said to be relativ^ely rather 

 large. In the foetus accessory spleens are found very frequently along the course of 

 the splenic vessels. On the other hand. Parsons seems to find the surface of the 

 spleen more regular than in later life. The fissures on the convex surface are less 

 frequent and less deep. The great size of the liver in the foetus brings the left lobe 

 into contact with the spleen. The relatively large suprarenal capsule nearly or quite 

 separates it from the left kidney. 



Accessory spleens ^ are common, but they are not all of the same signifi- 

 cance. Some are constricted parts of the spleen which have become separated, 

 mostly from the anterior border, and are connected with the organ only by fibrous 

 tissue. Others, found chiefly in the greater omentum near the hilum, are apparently 

 distinct masses of splenic tissue. Many of them, however, have no Malpighian 

 corpuscles, are intermediate between the spleen and the lymph-nodes, and, proba- 

 bly, are to be classed as haemolymph-glands. They are said to be found some- 

 times within the pancreas. It is not impossible that certain irregular nodules occa- 

 sionally found on the spleen near the hilum are due to the fusion of such accessory 

 spleens. Otto has seen twenty-three accessory spleens in one body. They are 

 usually of the size of a pea. 



Surface Anatomy. — The relations of the spleen to other organs have been 

 described, but it should be stated that the phrenic surface lies beneath the ninth, 

 tenth, and eleventh ribs (sometimes the eighth also), and that its long axis is that of 

 the shafts of these ribs. It is important to note that the spleen is situated behind the 

 stomach rather than to the left of it, so that in general language the organ is more in 

 the back than in the flank. The highest level of the spleen is opposite the body of 

 the ninth thoracic vertebra, and its lowest opposite that of the first or second lumbar. 

 A line from the top of the sternum to the tip of the eleventh rib should be entirely 

 anterior to the spleen. 



PRACTICAL CONSIDERATIONS : THE SPLEEN. 



The spleen may be congenitally absent, or it may be of extremely small size, — 

 no larger than a walnut ; or there may be superyizimerary spleens connected with the 

 main gland ; or there may be multiple spleens entirely separate and lying in the 

 folds of the greater omentum, the gastro-splenic omentum, or the transverse meso- 

 colon. It is conceivable but unlikely that these anomalies may lead to mistaken 

 diagnoses. 



The outline of the normal spleen is difficult of accurate determination by either 

 palpation or percussion because {a) it is covered in front by the stomach, the cardiac 

 end of which — if the stomach is distended — completely overlaps it ; (3) posteriorly 

 it is covered at its lower portion by the diaphragm and by the tenth and eleventh 

 ribs and the thick muscles overlying them, and at its upper portion by the same 

 muscles, the diaphragm, the ninth rib, the pleura, and the lung ; (V) inferiorly it is 

 in contact internally with the upper end and part of the outer edge of the left kidney, 

 and externally with the splenic flexure of the colon ; {d') the upper part of the 

 phrenic surface is occasionally in contact with the left lobe of the liver (Ouain) ; (^) 

 it is the most variable in both shape and size of all the abdominal viscera ; (/) it 



' Archiv f. mikro. Anat., Bd. Ivi., 1900. 



"^ Consult articles by Parsons and by Haberer, just noted. 



