THE DUCTLESS GLANDS. 



411 



posed of vesicles, or sacculi, either simple and closed, as in 

 the thyroid (fig. 106), and supra-renal capsules, or 

 variously branched, and with the cavities of the several 

 branches communicating in and by common canals, as in 

 the thymus (fig. 107). These vesicles, like the acini of 

 secreting glands, are formed of a delicate homogeneous 

 membrane, are surrounded with and often traversed by a 

 vascular plexus, and are filled with finely molecular albu- 

 minous fluid, suspended in which are either granules of 



F/V. 106.* 



fat, or cytoblasts or nuclei, or nucleated cells, or a mixture 

 of all these. 



Structure of the Spleen. The spleen is covered exter- 

 nally 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 connec- 

 tive tissue, with a large preponderance of elastic fibres, 

 forms the immediate investment of the spleen. Prolonged 

 from its inner surface are fibrous processes or trcibecula, 



* Fig. 106. Vesicles from the Thyroid Gland of a Child (from K61- 

 liker) ". a, connective tissue between the vesicles ; b, capsule of the 

 vesicles ; c, their epithelial lining. 



