36 SECRETION. 



glands, the pancreas, the lachrymal glands, and the mam- 

 mary glands. 



5. Ductless , or Hood-glands. Examples of these are the 

 thymus, the thyroid, the supra-renal capsules, and the spleen. 



The liver is a glandular organ which cannot be placed in 

 any one of the above subdivisions, as we shall see when we 

 treat specially of its anatomy. The lymphatic glands and 

 other parts connected with the lymphatic and the lacteal 

 system are not embraced in the above classification. 1 These 

 are sometimes called conglobate glands. 



The general structure of secreting membranes and the 

 follicular glands is very simple. The secreting parts consist 

 of a membrane, generally homogeneous, on the secreting sur- 

 face of which are found epithelial cells, either tesselated 

 or of the variety called glandular. Beneath this mem- 

 brane ramify the blood-vessels which furnish the elements 

 of the secretions. The follicles are simply digital inversions 

 of this structure, with rounded, blind extremities, the glan- 

 dular epithelium lining the tube. 



The tubular glands have essentially the same structure 

 as the follicles, except that the tubes are long and more or 

 less convoluted. The more complex of these organs contain 

 connective tissue, blood-vessels, nerves, and lymphatics. 



The compound racemose glands are composed of branch- 

 ing ducts, around the extremities of which are arranged 

 collections of rounded follicles, like bunches of grapes. In 

 addition to the epithelium, basement-membrane, and blood- 

 vessels, these organs contain connective tissue, fibro-plastic 

 elements, lymphatics, involuntary muscular fibres, and nerves. 

 In the simple racemose glands the excretory duct does not 

 branch. 



The ductless glands contain blood-vessels, lymphatics, 

 nerves, sometimes involuntary muscular fibres, fibro-plastic 

 elements, and a peculiar structure called pulp, which is com- 



1 For the anatomy of the lymphatic system, see vol. ii., Absorption, p. 439, 

 et seq. 



