462 PKOF. HUXLEY ON THE CLASSIFICATION OF BIRDS. [Apr. I I, 



divided by the structure of the skull, described above, into two groups 

 — the one containing the Pelicans, the other the remaining genera. 



•h 5. The Aetomorph^. 



The rostrum is more or less arched and hooked at the tip, and at 

 its base there is a cere in which the nostrils are pierced. Basipteiy- 

 goid processes may be present or absent. The maxillo-palatine pro- 

 cesses may be concavo-convex lamellae, or may be spongy and fill up 

 the base of the rostrum, but they are always united with an ossifi- 

 cation of the septum. 



The breadth of the articular surface at the distal end of the qua- 

 drate bone is greater than its length, the outer condyle extending 

 about as far downwards as the inner. 



The angle of the mandible is never recurved. 



The sternum is broad, and has a strong carina. Its posterior edge 

 may be entire, or may have one or two notches on each side. 



The pelvis and the tarso-metatarsus vary greatly. The feet always 

 possess a hallux ; the fourth toe is never permanently turned back- 

 wards, and the anterior toes are never completely or even largely 

 webbed. In other respects they vary. 



There are always two carotids. 



The inferior larynx may be wanting, and when developed has not 

 more than one pair of intrinsic muscles. 



The circlet of feathers may be present or absent upon the oil- 

 gland ; and the contour feathers have, or have not, an aftershaft. 



The division of the Aetomorphas is equivalent to the " Raptores " 

 of Cuvier — an eminently natural assemblage, and yet one the mem- 

 bers of which, as the preceding enumeration of their characters 

 shows, vary in most important particulars. 



They appear to me to fall naturally into four well-defined primary 

 groups — the StrigidcB, the Cathartidce, the Gypaetidce, and the 

 Gypogeranidce. I3ut this arrangement is so different from that or- 

 dinarily adopted, that I shall proceed to justify it by enumerating 

 the principal circumstances in which the members of the several 

 divisions agree with one another and differ from the rest. 



In the Strigidce, or Owls, the feathers want the aftershaft, and the 

 oil-gland is not surmounted by a circlet of feathers. The hallux is 

 more than half as long as the fourth toe, and on a level with the 

 other toes. The claws are long, curved, and acute, and the fourth 

 toe is reversible. 



The first three phalanges of this toe are subequal and very short ; 

 all three together are not so long as the penultimate phalanx. 



The basal phalanx of the third toe is not longer than the second, 

 and is far shorter than the penultimate. 



The tarso-metatarsus is extremely flattened, with strong lateral 

 ridges, the inner edge being particularly thin ; and, usually, there is 

 an osseous loop for the extensor tendons on its front face. 



