504 



THE NATURE BOOK 



nomer. There is a general tendency 

 amongst the unobservant to regard crea- 

 tures with small eyes as blind. " Blind as 

 a bat " is proverbial, and " blind mouse " 

 (=:shrew mouse) still holds its ground in 

 the north. 



From the brittle nature of his tail (a 



ip— —" 



involve such injury to the surrounding 

 integument as would cause the tail to 

 drop short off. Experiment showed that 

 his objection to the view previously held 

 was well founded. A hzard's tail which 

 is subjected to violence does not break 

 across a vertebra, but between two 

 vertebrae. The fracture is con- 

 fined to the skin, the remainder of 

 the accident being a dislocation. 

 That comparatively slight violence 

 is necessary to produce a complete 

 dislocation is due to a peculiar 

 arrangement of the tail muscles. 

 As can be seen from the photo- 

 graphs, the muscles of the centre 

 fragile portion of a hzard's tail are 

 arranged round it lengthways in 

 successive groups of eight — two 

 muscles in each group being to- 

 wards the upper surface, two on 

 the right, two on the left, and two 

 on the under surface. The proximal 

 ends (those nearest the body) of 

 these muscles fit somewhat weakly 

 into sheaths; the chstalends (those 

 fiu'thest from the body) are firmly 

 attached to the vertebrae and the 

 skin. In a dislocation of the tail 

 the scales are wrenched apart, the 

 skin broken, the muscles whipped 

 out of their sheaths, and the verte- 

 bra to which their distal ends are 

 attached parted from the vertebra 

 which immediately precedes it. An 

 end-on view of the portion which a 

 characteristic which is pecuhar to lizards) hzard leaves behind him presents, to some 

 the Slow-Worm gets his distinguishing extent, the appearance of a sea-anemone, 

 epitliet fragilis. For a description of the and this appearance is heightened when, 

 anatomical structure which makes dis- as in one of the illustrations, the eight 

 location of a lizard's tail not only hkely dislocated muscles are spread out. The 



THE NORMAL TAIL DISLOCATION OF A LIZARD, 



1. Three vertebra; «" '■''" between two dislocations of a Lizard's 



tail. It should be noted that they are not broken, and that 

 each vertebra corresponds in length to two rows of scales. 



2. A single vertebra of a Lizard's tail, showing the weak spot, a 



partially ossified slit, where it used to be supposed that 

 fracture normally occurred. 



3. A portion of a Lizard's tail showing a secondary out-growth 



(false tail) from a point on the upper surface where there 

 has been some injury. 



at certain definite spots, but inevitable 

 if sufficient violence be employed, I must 

 refer the reader to Dr. (now Professor) 

 Leighton's excellent book on British 

 Lizards, and I must content myself here 

 with a resume of his investigation. 



Before this investigation was pubhshed 

 it was generally supposed that the brittle- 

 ness of a lizard's tail was due to the 

 existence of a weak spot in each of the 

 tail vertebrae. This weak spot takes the 

 form of a transverse spht which is in- 

 completely ossified. It occurred to Pro- 

 fessor Leighton that the fracture of a 



portion which a lizard retains reveals the 

 distal end of a vertebra surrounded by 

 the cavities into which the muscles of 

 the lost portion fitted. In the Sand Lizard 

 and the Common Lizard the points liable 

 to dislocation can be easily determined 

 from the fact that two scales go to one 

 vertebra. Given, therefore, one disloca- 

 tion, further dislocations can easily be 

 produced at intervals of two scales from 

 it. To the naturalist who is left with a 

 lizard's tail in his hand (where he would 

 fain ha^•e held a lizard), I would recommend 

 as consolation the proof, if further proof 



weakened vertebra would not necessarily be necessary, of Professor Leighton's inter- 



