No. 2.j ON THE GUSrATORV ORGANS. 153 



usual, are smallest about the tip. The circumvallate papillae 

 are three in number. They are arranged in an isosceles (or 

 more rarely an equilateral) triangle, the base of which measures 

 4.6 mm. The apex of the triangle is turned towards the epi- 

 glottis, and is distant some 12 mm. from the base of the tongue. 

 The posterior papilla is situated directly in the middle line of 

 the organ, and is much larger than the anterior papillae. The 

 region behind the triangle formed by the circumvallate papillae 

 lacks the usual fleshy elevations, and is quite smooth ; the 

 immediate area around the papillae, however, is more or less 

 papillate. The lateral organs of taste (papillae foliatae) were so 

 effectually concealed that the superficial examination of the 

 tongue failed to reveal their presence. At each side of the 

 tongue, just above the line of union of the upper and lower 

 surfaces, is a fringe of rather coarse filiform papillas, curving 

 upwards, inwards, and backwards. The fringe terminates 

 before reaching the base of the glosso-palatine arch. 



The tongue of a young Didelphys presented some points of 

 interest. This organ was 19 mm. in length and 7 mm. in 

 breadth. The dorsum was marked anteriorly by a longitudinal 

 mesial raphe. The raphe disappeared about 12 mm. from the 

 tip. The tip was rounded, and fringed with simple papillae as 

 in the adult organ. The circumvallate papillas were arranged in 

 the usual triangle, but were very closely set and very near the 

 base of the tongue. The lateral fringe of filiform papillae at 

 the back of the tongue was well marked. 



The Mechanical PapillcB. — The general surface of the tongue, 

 anterior to the triangle formed by the circumvallate papillae, is 

 covered with compound filiform papillae. Interspersed among 

 them are a lesser number of filiform papillae of a simple type. 

 About the tip, where the papillae are smaller and more closely 

 set, there appear to be about thirty to the square millimetre of 

 surface. Posteriorly there are only half that number covering 

 the same area. Each papilla rests upon one or more papillary 

 upgrowths of the mucosa, and, at a short distance from its base, 

 breaks up into a varying number of very long, slender, recurved 

 secondary papillas or processes. The number of these processes 

 varies greatly even in the same region. There are seldom less 

 than ten, and I have seen more than fifty. The average num- 

 ber appears to vary from sixteen to twenty. The free portion 



