318 GENERAL ANATOMY. 



cellular membrane, and some with a fibrous one, some of 

 which are surrounded by a serous membrane, and others by a 

 great deal of cellular and adipose tissues. The internal face of 

 this membrane is continuous with the cellular tissue, more or 

 less loose, which exists abundantly in the glands. 



These organs have many sanguineous and lymphatic vessels, 

 and few nerves: more, however, than the mucous membrane 

 generally, but less than the skin. The greater number re- 

 ceive only arterial blood ; the liver alone in man and the maYn- 

 miferous animals, the liver and kidneys in oviparous animals, 

 receive venous blood besides, which explains the nature of 

 the liquids, so different from the blood, and altogether excre- 

 tory, furnished by these glands. The number and volume, or 

 the total capacity of the arteries, are very different in the 

 glands, but nowhere greater than in the kidneys. The length, 

 course and mode of distribution of the vessels are also very 

 various. The difference of capacity between the arteries and 

 veins is very little discernible in the glands; and, in fact, the 

 greater part of the blood in them is transformed into secreted 

 humour, and conveyed away by the excretory canals. 



486. These ducts commence by very fine, invisible, and 

 probably closed radicles, which unite with each other in the 

 manner of the veins, to form several trunks, as in the lachry- 

 mal, sublingual and mammary glands, or one alone, as in all 

 the other glands besides. These canals, either many, or single 

 for each gland, generally take a straight course, in the testicles 

 excepted, where it is tortuous, and terminate on the tegu- 

 mentary membranes. That of the ovary is alone interrupted; 

 those of the rnammse present, before their termination, oval 

 enlargements; those of the kidneys present at first an enlarge- 

 ment or pelvis, and then terminate in a single bladder for 

 both; that of the liver and that of each testicle have also a re- 

 servoir, but situated laterally, and to reach which the secreted 

 liquid is obliged to take a retrograde course. The canals of 

 the other glands present neither interruption, enlargements, 

 nor reservoirs. 



The composition of the excretory ducts is always the re- 

 sult of a mucous membrane whose thickness diminishes in 



