THE GOITRE. 221 



coming cartilaginous, the extremities reaching to the 

 abdomen. In excitement the front portion of the os 

 hyoides is drawn backwards towards the abdomen ; 

 by which action, the cartilaginous extremities remain- 

 ing fixed, the slender elastic horns are forced out in 

 a bowed form, carrying with them the extensile skin 

 with its two internal surfaces in contact, forming a 

 thin lamina, frequently so far projected as to consti- 

 tute half of a long ellipse with an obHque base. When 

 the bone is relaxed it resumes its straight direction 

 by its own elasticity, and the goitre shrinks up again 

 under the throat so as to be scarcely visible. 



The changes of colour for which these little rep- 

 tiles are remarkable, are often stated to take place 

 with special intensity on the goitre, which is said to 

 present an endless succession of ever varying hues. 

 This also is entirely a mistake. The extensible skin, 

 which forms the goitre, is always of one permanent 

 hue, generally some rich tint of red or yellow. In 

 A. iodurus and oj)alinus, the two species before us, 

 the colour is a brilliant orange or red-lead, becoming 

 pale towards the margin, so as not at all to be per- 

 ceived when the skin is relaxed, the edge itself 

 being whitish, like the rest of the breast and belly. 

 This alternate appearance and disappearance of the 

 bright colour has no doubt been mistaken by careless 

 observers for changes of hue. The scales which 

 cover the goitre are whitish like those on the neigh- 

 bouring parts ; they lie close together in the relaxed 

 state of the skin, but when the latter is stretched, 

 the little white pointed scales are widely separated, 



