450 PERCHING BIRDS 



extent by the bird itself, although it is never entirely chiselled out 

 after the manner of the woodpeckers. The pure white eggs, which 

 measure more than half an inch in length, arc laid in May on the chips 

 at the bottom of the hole without anything in the shape of a nest ; the 

 number in a clutch usually ranging from six to eight, but occasionally 

 reaching half-a-score. 



The whole of the remaining representatives of the 



^ , . , British bird-fauna are included in the great group of 



(Turdus musieus). , . , . , . . , , t^ / 



perchmg bu'ds, constitutmg the order rasseres (or 



Passeriformes) of ornithologists, so called from the Latin name of 

 the sparrow, the typical member of the entire assemblage. In place of 

 commencing the series with that species, it is, however, preferable 

 to take first the thrush, throstle, or mavis, and its relatives ; for this 

 tribe of perching birds, typifying the family Turdida^, although at one 

 time regarded as the most specialised representative of the group, is 

 really the most generalised, that is to say, the one which comes nearest 

 to the ancestral type. 



In the case of the British bird-fauna, at any rate, there is very 

 little difficulty in recognising a perching bird, especially when we have 

 eliminated the " picarian " group, of the various representatives of which 

 the leading characteristics have just been given. It may be mentioned, 

 however, that the best definition of a passerine bird is based upon the 

 combined characteristics afforded by the form and mode of arrange- 

 ment of the bones of the palate of the skull and the relations of the 

 tendons forming the terminations of the deep-seated muscles on 

 the lower surface of the foot. It will be unnecessary here to 

 particularise the structure of the palate ; but it may be mentioned that 

 in the foot the hind-toe is served by a single tendon, quite distinct 

 from the one which splits into three branches to supply the three front- 

 toes. Perching birds are represented by more than six thousand species, 

 of which between one hundred and forty and one hundred and fifty 

 have been recorded from the British Isles, although in some cases only 

 on one or two occasions. 



The colouring of the interior of the mouths of nestling perching 

 birds offers an almost unknown field of investigation. It has been 

 suggested that the bright-coloured membranous margins of the gape 

 are intended as a guide to the parents in feeding their offspring. In 

 addition to this, the interior of the mouth in most nestlings is bright 

 yellow, occasionally marked with black (hedge -sparrow) or white 

 (bearded titmouse) spots on the tongue and palate, and it seems that 



