AUKS. 531 



structure should not have been independently acquired in two distinct groups. 

 Moreover, the auks differ from the gulls in the absence of any projecting process 

 to the lower end of the humerus. 



In this wider sense the diving -birds are characterised externally by the 

 extremely backward position of their short legs, in which the front toes are either 

 completely webbed or lobed, the first toe being either absent or rudimentary. In 

 the skull the palate is of the cleft (schizognathous) type, the lower jaw is abruptly 

 truncated behind, and there are large grooves for the reception of glands on the 

 forehead, which are separated from one another merely by a narrow ridge. 

 The humerus has no process at its lower end; but the tibia has an upwardly 

 projecting crest, which may unite with the knee-cap or patella to form a long 

 spike projecting upwards in front of the femur. The young are born covered with 

 down or feathers, and are soon active. In the plumage, the spinal feather-tract is 

 either forked on the upper part of the back, or not defined on the neck ; while the 

 oil-gland is invariably tufted. The wings are relatively short ; and the beak is 

 comparatively straight and often much compressed, with its horny sheath generally 

 composed of but a single piece. 



Contrasted with the other ordinal groups in which the palate is of the cleft 

 type, the divers are readily distinguished from the tube-nosed birds by the normal 

 conformation of their nostrils, their active young, and the absence of a projecting 

 process to the lower end of the humerus; the latter feature, together with the 

 more marked upward extension of the crest of the tibia, and the lack of any 

 perforations in the bones of the second digit of the wing, differentiating them from 

 the gulls. They are not likely to be confounded with the Limicolce or any of the 

 remaining orders ; from all of which, except certain of the group named, they are 

 distinguished by the presence of grooves on the front of the skull. The group 

 may be divided into three families, of which the second and third are much more 

 closely related to one another than they are to the first. 



THE AUKS. 

 Family ALCIDuE. 



The auks are characterised externally by the absence of the first toe; 

 while in the skeleton the crest of the tibia is relatively short, the metatarsus is 

 not laterally compressed, and the vertebrae of the back are articulated together 

 by cup-and-ball joints. The front toes are fully webbed and furnished with 

 sharp, claw - like nails ; the tail, although short, is normal, and the beak, 

 although frequently much compressed, deep, and short, is subject to great 

 variation in form. The family includes the true auks, guillemots, pigrny-auks, 

 and puffins ; all of w^hich are marine, and confined to the colder regions of the 

 Northern Hemisphere. 



The typical members of the family are characterised by the large 

 The True Auks. . _ ., JL . / . . 



size ot the compressed beak, marked in rront by oblique grooves, 



and feathered at its base close up to the slit-like nostrils, which are almost 

 -concealed by a dense velvety feathering, completely filling the fossae in which 



