724 CARTILAGE. GLANDULAR STRUCTURES. 



together by intercellular substance, without vessels of any kind, 

 and are nourished by imbibition through their whole surface. — 

 There are many cases, however, in which the structureless Inter- 

 cellular substance is replaced by bundles of Fibres, sometimes 

 elastic, but more commonly non-elastic ; such combinations, which 

 are termed i^iiro-Cartilages, are interposed in certain Joints, 

 wherein tension as well as pressure has to be resisted, as for 

 example, between the Vertebrae of the spinal column, and the 

 bones of the Pelvis. — In examining the structure of Cartilage, 

 nothing more is necessary than to make very thin sections with a 

 sharp razor or scalpel, or with a Valentin's Knife (§ 136), or, if 

 the specimen be large and dense (as the cartilage of the ribs), with 

 the Section-instrument (§ 137). These sections may be mounted 

 in weak Spirit, in Goadby's solution, or in Glycerine- jelly ; but in 

 whatever way they are mounted, they undergo a gradual change by 

 the lapse of time, which renders them less fit to display the cha- 

 racteristic features of their structure. 



566. Structure of Glands. — The various Secretions of the body 

 (as the saliva, bile, urine, &c.) are formed by the instrumentality 

 of organs termed Glands ; which are, for the most part, constructed 

 on one fundamental type, whatever be the nature of their product. 

 The simplest idea of a Gland is that which we gain from an exami- 

 nation of the ' Follicles ' or little bags imbedded in the wall of the 

 Stomach ; some of which secrete Mucus for the protection of its 

 surface, and others Gastric juice. These little bags are filled with 

 Cells of a spheroidal form, which may be considered as consti- 

 tuting their Epithelial lining ; these cells, in the progress of their 

 development, draw into themselves from the blood the constituents 

 of the particular product they are to secrete ; and they then seem 

 to deliver it up, either by the bursting or by the melting-away of 

 their walls, so that this product may be poured-forth from the 

 mouth of the bag into the cavity in which it is wanted. The 

 Liver itself, in the lowest animals wherein it is found, presents 

 this condition. Some of the cells that form the lining of the 

 stomach in the Hydra and Actinia, seem to be distinguished from 

 ■the rest by their power of secreting Bile, which gives them a 

 brownish-yellow tinge ; in many Polyzoa, Compound Tunicata, and 

 Annelida, these biliary cells can be seen to occupy follicles in the 

 walls of the stomach; in Insects these follicles are few in number, 

 but are immensely elongated so as to form biliary tubes, which lie 

 loosely within the abdominal cavity, frequently making many con- 

 volutions within it, and discharge their contents into the com- 

 mencement of the intestinal canal ; whilst in the higher Mollusca, 

 and in Crustacea, the follicles are vastly multiplied in number, and 

 are connected with the ramifications of gland-ducts, like grapes 

 upon the stalks of their bunch, so as to form a distinct mass which 

 now becomes known as the Liver. The examination of the biliary 

 tubes of the Insect, or of the biliary follicles of the Crab, which 



