Ifa2 THE DUCTLESS GLANDS. 
Trabecular Framework (trabeculie lienis).—From the deep surface of the tunica 
propria numerous processes or trabeculee are given off, and these penetrate into the sub- 
stance of the spleen. Some are cord-like, others are in the form of flattened bands, and all 
are composed of fibrous tissue and involuntary muscular fibres. Within the spleen the 
trabeculee branch and re-branch, and join with each other to form a supporting framework 
for the organ. The blood-vessels, as they enter at the hilus, carry in with them connec- 
tive-tissue sheaths, and these also take part in the formation of the trabecular framework. 
Spleen Pulp (pulpa lienis).—The interstices between the strands of the trabecular 
framework are filled with spleen pulp. This is supported by a delicate reticulum formed 
by branching cells. The spaces of the network freely communicate, and are occupied by 
blood in which there are large numbers of leucocytes, and also large cells special to the 
spleen. These are termed splenic cells, and contain pigment, and not infrequently red 
blood corpuscles in their interior. 
Blood-vessels and Malpighian Corpuscles.—The splenic arteries, as they traverse the 
spleen, run in the trabeculee. The small branches ultimately leave these and enter the 
spleen pulp. As they do so they become ensheathed in a coating of adenoid tissue. At 
certain points in the course of the arteries this sheath suddenly increases in thickness, and 
forms small round or oval masses of adenoid tissue upon the vessel. In sections through 
the spleen these small nodular masses are visible to the naked eye as minute white spots. 
They are called Malpighian corpuscles (noduli lymphatici lienales). The artery rarely 
passes through the centre of such a corpuscle. As a rule the adenoid tissue is massed 
chiefly upon one side of the vessel, and a plentiful supply of blood is given to the nodule 
by means of a capillary network in connexion with the artery on which the Malpighian 
corpuscle is developed. 
The manner in which the minute terminal arteries end in the spleen pulp is peculiar. 
The wall becomes reduced to the endothelial lining, and the cells forming this gradually 
separate from each other and become continuous with those of the reticulum of the spleen 
pulp. The blood therefore flows directly into the meshes of the reticulum of the pulp. 
The minute radicles of the veins begin in the same way as the arteries end. The walls 
are gradually built up by the union of cells continuous with the open reticulum, and the 
blood flowing into the vessels so formed is led away towards the larger veins which occupy 
the trabecule. 
Development of the Spleen.—It is not until the second month of intrauterine 
development that the spleen begins to develop. It is formed from mesoderm, and appears 
in the dorsal mesogastrium in the neighbourhood of the pancreas. After a short time it 
becomes invaded by blood-vessels, but the Malpighian corpuscles are somewhat late in 
making their appearance. The spleen grows to the left in the direction of least resistance, 
protruding the left layer of the mesogastrium before it, and its form is determined by 
the pressure to which it is subjected by the neighbouring viscera and the abdominal wall. 
THE SUPRARENAL CAPSULES. 
The suprarenal capsules (glandule suprarenales) are two small flattened organs 
which lie in the epigastric region, one on either side of the spine, and in intimate 
relation to the upper end of the corresponding kidney. 
The right suprarenal capsule is, as a rule, triangular in form, and rests by its 
base upon the anterior and inner aspect of the upper end of the right kidney. It 
is placed between the posterior surface of the right lobe of the liver and that portion 
of the diaphragm which covers the side of the spine. 
The anterior surface, which looks outwards as well as forwards, presents two 
impressions—(1) The one is a narrow flattened strip adjoining the anterior border 
of the capsule which is overlapped by the inferior vena cava; (2) the second 
impression comprises the remainder of the anterior surface, and is in contact with 
the liver. Only a small and variable part of the lower portion of the anterior 
surface of the right suprarenal capsule is covered by peritoneum. On the upper 
part of the impression for the vena cava, not far from the apex of the capsule, a 
short fissure termed the hilus may be observed. From this issues a short wide 
vein which immediately enters the vena cava inferior. The posterior surface of 
the right suprarenal capsule is divided by a salient curved ridge into an upper flat 
part, which is applied to the diaphragm, and a concave lower part, which 1s 
oceupied by fat and rests upon the kidney. 
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