d 



84 GENERAL ANATOMY OF THE GLANDULAR SYSTEM. 



lobulated glands, viz. the lachrymal, mammary, salivary 

 glands, and the pancreas. Each acinus is not therefore, as was 

 supposed by Malpighi, Ruysch, and Mascagni, a single cell, 

 but a cluster of cells, too minute to be seen, except in the dis- 

 tended state and by the aid of the microscope, seated upon the 

 extremity of a minute branch of the excretory tube, and sur- 

 rounded by a net-work of capillaries, exactly analogous in 

 structure to one of the mucous glands of the mouth, or of the 

 duodenum. Sometimes, instead of the short cells of the acini, 

 the ducts terminate in long excretory tubes, as in the kidney 

 and testis, when the length of the tube compensates in regard 

 to the extent of secretory surface, for the nondivision into cells. 

 In some glands, as in the liver of man and all the vertebrate 

 animals, and in the kidneys of oviparous animals where there 

 is a portal circulation and the secretion is made from venous 

 blood, the arrangement is somewhat peculiar. The ducts 

 ramify irregularly, present no arborescent arrangement, and 

 there is no distinct division into separate lobules. The excre- 

 tory ducts terminate in the acini, in the form of tufts of micro- 

 scopical tubes, which anastomose together so as to form a sort 

 of net-work in the body of the acinus : the centre of each aci- 

 nus, in the peculiarly constructed gland called the liver, being 

 occupied by a vein, according to Kiernan,* which carries away 

 the blood of the portal system, after its excrementitious parts 

 have, by the secretory action, been transferred to the branches of 

 the excretory duct in order to be thrown into the duodenum as bile. 



Capillary Blood-Vessels. 



The excretory ducts of the liver and kidneys are considered 

 the most minute; yet these have a diameter two or three times 

 as large as the minute arteries and veins, which may be seen with 

 the microscope, ramifying on the ducts and forming a capillary 

 net-work on their walls and interstices, and from which the 

 fluids are distilled into the cavities of the tubes, modified in 

 different parts, so as to constitute the peculiar secretions. 

 Thus, in the kidney and testis, the ducts are arranged in con- 



* See Anatomy of Liver. 



