| OCR Text |
Show 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 developed 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 Ratitae 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 vertebrae with the anterior 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 ordinary three digits ; and two of these, the radial and the middle, are provided with claws -j*. 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 precaudal]; vertebras. 11. The feathers being devoid of aftershafts. * By the term " maxillo-palatines " I designate those processes of the maxillary 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 maxilla*: of which they form a part, under the head ofprevomers. 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. f 1 regard as " caudal" all those vertebras of the bird's complex " sacrum " which lie behind the exit of the roots of the sacral plexus. The foremost of these caudal vertebras are readily distinguished from the proper sacral vertebras, which immediately precede them, by possessing inferior transverse processes, or, more strictly speaking, anchylosed ribs, which, like flying buttresses, pass from the bodies of the vertebras upwards and outwards to the roof of the " sacrum " at its junction with the ilium. |
