62 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



(b) Compound alveolar or racemose sali- 

 vary glands, mammary gland, lung, 

 pancreas, sebaceous glands. 



Glands not included in this classification are uni- 

 cellular glands and secreting membranes, which can- 

 not be classified as to form. Lymph glands, which 

 are of connective-tissue origin, and like the testis or 

 ovary, may be called dehiscent or cytogenic glands. 

 Follicular glands, such as the thyroid gland, and the 

 ductless glands, producing internal secretions, such 

 as the hypophysis cerebri, thyroid gland, suprarenal 

 gland, areas of Langerhans of the pancreas, inter- 

 stitial cells of the testis, and corpora lutea of the 

 ovary. The thymus gland and spleen are lymphoid 

 organs, and therefore to be classified among the 

 lympho glandule? . 



The object of any anatomical classification is to 

 simplify and correlate structural facts. From the 

 foregoing outline it is clear that glands, according to 

 modern views, embrace such a complex of structures 

 that any classification, either according to origin, or 

 form, or tissues, or even function, does not accom- 

 plish the end in view, namely, simplicity. The dif- 

 ficulty met with is due to the fact that our con- 

 ception of a gland rests largely with the physiolog- 

 ical action of gland cells rather than with any com- 

 mon intrinsic anatomical quality. 



Endothelium. This term, introduced by His in 

 1865, is generally applied to the layer of cells that 

 line closed cavities, such as peritoneal and pleural 

 cavities, circulatory system, and cavities of joints. 



