404 MANUAL OF HISTOLOGY. 



adherent to the fibrous coat beneath it, and closely invests the 

 organ. It is reflected off at the hilum to form the gastro- 

 splenic omentum, and also at the upper border, where it in- 

 vests the suspensory ligament. 



The fibrous coat, or. capsule of the spleen, is white in color, 

 and thicker than the serous coat. It is composed of fibrous 

 tissue, which is permeated very extensively by elastic fibres. 

 Mingled with them are a few smooth, muscular elements. At 

 the hilum this fibro-muscular coat surrounds the vessels and 

 nerves and passes into the substance of the spleen with them, 

 forming what is called the "capsule of Malpighi." It invests 

 the arteries and veins as far as their finer branches, and gives 

 off fibrous processes, which have a diameter of -fa mm. to 

 2 mm., and which help to make up the trabecular frame- 

 work of the spleen. This framework is formed by processes 

 sent off from the internal surface of the spleen's fibrous coat, 

 which join with the processes sent off from the capsule of 

 Malpighi, and interlace until a firm network is made. In this 

 structure lie embedded the spleen-pulp and the Malpighian 

 corpuscles. The fibrous sheath of the veins has a somewhat 

 peculiar arrangement. It becomes at once intimately adherent 

 to the venous walls, uniting them closely with the surrounding 

 parenchyma. As the veins grow smaller this fibrous coat splits 

 into bands containing muscle-cells, which lie longitudinally 

 along the vessel-wall. These bands do not entirely surround 

 the vessel, however, but allow the thin endothelium and in- 

 tima to be seen between them. They finally leave the veins 

 to join the trabecular framework. The tissue composing this 

 framework is made up, like the capsule, of elastic and other 

 fibres, with a good many smooth muscle-fibres arranged longi- 

 tudinally along their course. 



MalpigMan corpuscles. The Malpighian or spleen corpus- 

 cles are so intimately connected with the arteries that it will 

 be necessary first to trace in part the course of the latter. The 

 arteries of the spleen enter at the hilum, enclosed in a common 

 sheath with the veins and accompanied by the lymphatics. 

 They divide and subdivide very rapidly. When they have 

 reached a diameter of about two-tenths of a millimetre, the 

 veins leave them and take an independent course. At this 

 point of separation, or even sooner, the outer connective-tissue 

 coat of the artery begins to be transformed into the ordinary 



