CHAPTER XIII. 



THE VASCULAR GLANDS. 



IN addition to the various glands the structure and functions of which 

 have heen considered in the preceding chapters, and which have been 

 shown either to secrete from the blood materials of use in digestion or 

 to excrete from the blood materials of no further use in the economy, 

 there are others which have not to do with secretion or excretion, at all 

 events directly. These are called Vascular glands, and comprise the 

 Spleen, the Thymus gland, the Tonsils, and the Solitary and Agminated 

 glands of Peyer in the intestine, all of which are made up chiefly of 

 lymphatic tissue, resembling lymphatic glands, and which are evidently 

 closely connected with the lymphatic system; the Supra-renal capsules 

 or Adrenals; the Thyroid gland; the Pineal and Pituitary glands and 

 the Carotid and Coccygeal glands. 



The Spleen. 



The spleen is the largest of these so-called vascular glands; it is situ- 

 ated to the left of the stomach, between it and the diaphragm. It is of 

 a deep red color, of a variable shape, generally oval, somewhat concavo- 

 convex. Vessels enter and leave the gland at the inner side or hilus. 



Structure. The spleen is covered externally almost completely by a 

 serous coat derived from the peritoneum, while within this is the proper 

 fibrous coat or capsule of the organ. The latter, composed of connective 

 tissue, with a large preponderance of elastic fibres, and a certain propor- 

 tion of unstriated muscular tissue, forms the immediate investment of 

 the spleen. Prolonged from its inner surface are fibrous processes or 

 trabeculcz, containing much unstriated muscle, which enter the interior 

 of the organ, and, dividing and anastomosing in all parts, form a kind 

 of supporting frame-work or stroma, in the interstices of which the 

 proper substance of the spleen (spleen pulp) is contained (Fig. 264). At 

 the hilus of the spleen, the blood-vessels, nerves, and lymphatics enter, 

 and the fibrous coat is prolonged into the spleen-substance in the form 

 of investing sheaths for the arteries and veins, which sheaths again are 

 continuous with the trabeculce before referred to. 



The spleen-pulp, which is of a dark-red or reddish-brown color, ia 



