426 AVES. 



united at their roots by a short membrane, Ciconia (g) ; and 

 those in which this membranous connection is confined to the 

 middle and outer toes. The short wading legs of the swimming 

 birds, as well as those with long wading legs present with regard 

 to the structure of their feet the following types : Swimming 

 feet, in which the three anteriorly directed toes are connected 

 as far as their extremities by an undivided swimming membrane 

 or web. Anas {i) ; half-swimming feet when the web only reaches 

 to the middle of the toes, Recurvirostra (k) ; split swimming feet 

 when the toes have an entire cutaneous border, Podicipes (l) ; 

 lobed feet when the border is lobed at each joint, Fulica (m) ; 

 sometimes the hind toe is included in the web-membrane, Phae- 

 thon {n) ; finally the hind toe may be completely absent in 

 some wading birds. In the Raiitae the inner toe is always absent, 

 and in the ostrich the second digit as well. 



Colour is highly developed in the feathers of birds and in some 

 cases in the skin of the head and neck (combs, wattles). It is 

 due either to pigments (absorption colours), or to the structure 

 of the parts acting upon the light after the fashion of a prism or 

 of thin plates (metallic lustre, iridescent colours). Sometimes 

 these two causes combine and produce wonderful effects as in 

 the humming birds, peacock, etc. The blacks, browns, reds, 

 yellows and rarely greens may be due to pigment ; blues and 

 violets are due to pigment and structure, there being no blue 

 pigment in birds. In the Touracos {3Iusophagidae) there is a 

 red pigment called turacin, which is soluble in water and washes 

 out of the feathers, colouring the water when the animal gets 

 wet or bathes ; the birds regain the colour when dry. It is 

 stated that the colour of fully grown feathers, in which the pulp 

 is dry, can in some cases change. 



The brain-case (Fig. 237) is arched and spacious, and, except 

 in the Ratitae and one or two other groups, the bones become 

 early fused together and the sutures obliterated. The orbits are, 

 except in Apteryx, very large. There is a well-marked inter- 

 orbital septum and the facial part of the skull is prolonged into 

 a beak consisting mainly of the premaxillary bones. The infra- 

 temporal arcade is complete, the rod-like jugal {J) and quadrato- 

 jugal (Q j) reaching back to the quadrate {Q). The supra- 

 temporal arcade is usually incomplete, but in some birds, e.g. 

 the fowl, the squamosal sends forward a process which joins the 



