ORGANS OF SECRETION. 605 



structure of the gland, and the minute terminal vesicles of 

 the ultimate tubuli appear clustered in racemose groups 

 forming small lobules or acini. The parotid, submaxillary 

 and sublingual salivary glands attain the greatest develop- 

 ment in the herbivorous quadrupeds where there is longest 

 mastication and the coarsest food ; they are smaller in the 

 carnivorous tribes where there is less mastication and richer 

 food, and they are deficient in the cetacea where the moist 

 food is mostly swallowed entire. 



The liver begins in man and mammalia, as in other ver- 

 tebrata, by a simple follicular protrusion, like the embryo 

 condition of the pancreas, from the anterior median surface of 

 the yet short straight intestine. Its parietes thicken to cons- 

 titute a soft vascular blastema, and new follicles and ramified 

 tubuli are prolonged through the substance of this deciduous 

 formative nidus. The primitive follicle becomes narrow and 

 elongated to form a duct, and thus to separate the gland from 

 the surface of the intestine, the duct develops a small filiform 

 diverticulum, which widens and elongates to form a gall- 

 bladder and cystic duct. And in the adult state of this most 

 complicated of all glands, in this highest class of animals, 

 where the tubuli have arrived at their maximum of sub- 

 division, they are still perceptible, larger than capillary 

 blood-vessels, constituting in groups the acini and nearly 

 the entire mass of this large organ, and when success- 

 fully inflated with air, their shut ends have appeared to 

 Krause to form minute dilated vesicles, like the lungs and 

 most other glands. The arrangement of the minute ccecal 

 tubes, forming the lobules or acini by their grouping, is 

 perceptible on the outer surface of the liver through the 

 transparent peritoneal covering, or on cutting open the larger 

 trunks of the vena portee or venae hepaticee and carefully 

 inspecting their inner transparent parietes. This minute 

 lobulated appearance, seen on all the peripheral parts of the 

 liver, was shown by Malpighi to be produced by the innu- 

 merable small ramifications of the proper secreting ducts, 

 which he found to constitute the essential part and the mass 

 of all secreting glands, and which here generally assume the 

 symmetrical forms of foliaceous or pinnated expansions of 

 small white cylindrical secerning tubuli, in all parts of the 

 organ. Into these minute terminal follicles, and their con- 

 necting continuous secerning trunks, the bile is transuded 



