1867.] PROF. HUXLEY ON THE CLASSIFICATION OF BIRDS. 419 



6. The barbs of the feathers are disconnected. 



7. There is no inferior larynx, and the diaphragm is better deve- 

 loped than in other birds. 



Though comparatively but few genera and species of this order 

 now exist, they differ from one another very considerably, and have a 

 wide distribution, from Africa and Arabia over many of the islands 

 of Malaisia and Polynesia to Australia and South America. Hence, 

 in all probability, the existing Ratitse are but the waifs and strays 

 of what was once a very large and important group. 



The Afro-Arabian genus Struthio is the type of one group of 

 this order, characterized by : — 



1. The prolongation of the maxillary processes of the palatine 

 bones forwards, beneath the maxillo-palatines*, as in most birds. 



2. The thickening of the inner edges of the maxillo-palatines, and 

 their articulation with facets upon the sides of the vomer. 



3. The shortness of the vomer, which does not articulate with 

 either palatines or pterygoids posteriorly. 



4. The slight, or wanting, ossification of the prefrontal processes 

 of the primordial cranium. 



5. The union of the bodies of the sacral vertebrse with the ante- 

 rior ends of the pubes and ischia. 



6. The presence of two shallow notches, on each side, in the 

 posterior margin of the sternum. 



7. The proportions of the fore limb. The humerus is about equal 

 in length to the distance between the pectoral arch and the ilium, 

 and is therefore much longer than the scapula. The antebrachium 

 is not half as long as the humerus. The manus possesses the ordi- 

 nary three digits ; and two of these, the radial and the middle, are 

 provided with claws f. 



8. The union of the pubes in a symphysis. 



9. The abortion not only of the hallux, but also of the distal end 

 of the metatarsal bone and of the phalanges of the second digit of the 

 foot, whence the foot is two-toed. 



10. The presence of thirty-five precaudalj vertebrae. 



1 1 . The feathers being devoid of aftershafts. 



* By the term " maxillo-palatines " I designate those processes of the maxil- 

 lary bones which extend, more or less horizontally, inwards and contribute to the 

 formation of the roof of the mouth and the anterior and inferior walls of the 

 nasal chambers. Nitzsch called them " Muscheltheile." Mr. Parker has included 

 them, with the maxillaj of which they form a part, under the head of prevomers. 

 I conceive these maxillo-palatine processes to answer to the palatine processes 

 of the maxillary bones in the Mammalia. 



t This interesting fact was first noted by Nitzsch (' Osteografische Beitrage,' 

 p. 91), but has since been forgotten. 



I 1 regard as "caudal" all those vertebraj of the bird's complex "sacrum" 

 which lie behind the exit of the roots of the sacral plexus. The foremost of these 

 caudal vertebrae are readily distinguished from the proper sacral vertebrae, which 

 immediately precede them, l)y possessing inferior transverse processes, or, more 

 strictly speaking, anchylosed ribs, which, like flying buttresses, pass from the 

 bodies of the vertebrae upwards and outwards to the roof of the " sacrum " at its 

 junction with the ilium. 



