280 Dr. Waller's Microscopic Exa7nination of the 



more closely, vve must use the higher powers of the compound 

 microscope, which the transparency ot' the membrane permits. 



The papillas conicoe of the frog consist of small elevations 

 of an irregular form, dispersed over the whole surface of the 

 tongue. They may generally be regarded as consisting of 

 small cones or cylinders, two or more of which are joined by 

 a common stem to the mucous membrane. They are com- 

 pletely covered with scales of epithelium, and frequently appear 

 to have sn)all apertures upon their surface, as if leading to some 

 cavity within them. In some, this opening is a small elongated 

 depression at the apex of the papilla; in others it is sharp 

 and well-defined, and below it some scales of epithelium ap- 

 pear lining the commencement of the papillary duct. When 

 the tongne is much distended, these papillae almost entirely 

 disappear, as if they were simply formed of rugae or folds of 

 the mucous membrane. They present no appearance of cir- 

 culation. At different ages of the animal they vary considera- 

 bly. In the young they are smaller and more transparent than 

 in those full-grown, where they are generally like truncated 

 cones, distinct Irom one another. At their summit the elon- 

 gated aperture already mentioned is generally seen. In the 

 Philosophical Magazine one of the most common appearances 

 ot these papillae is represented. 



The fungiform papillae, which are so easily distinguished 

 from the former by their active circulation, deserve principally 

 to arrest our attention. The blood, which when seen with the 

 lower power appeared to move within a small cavity, without 

 being contained in any capillary, is found, on being subjected 

 to higher power, to circulate within the usual canals, which 

 are coiled up into a very small space, so as to cause the blood 

 to trace a very circuitous route before it is enabled to make 

 Its exit. The exact course which it takes may often be traced 

 where the circulation is languid, by the gradual progress of the 

 blood-discs. The coil is connected with two and sometimes 

 with three small vessels, which supply it with blood. No dif- 

 ference can be detected between these supplying vessels, either 

 with regard to calibre or thickness. They are to be considered 

 as part of the capillary network, and they are often seen to 

 convey the blood in opposite directions, when watched for a 

 few minutes. In most instances the supplying vessels arrive 

 from opposite points, and the circular papilla appears nearly 

 on a level with the rest of the membrane; but in others the 

 papilla is like a gourd or wide-necked flask with the larger end 

 pendent and free. The vessels then run close together, tra- 

 versing the neck, and after ascending upwards unite with the 

 coil. 



