BIRDS. 333 



tubercles of the inferior extremity of the tibia. Most birds have 

 four toes, three anterior and one posterior. This last toe, named 

 the posterior thumb (hallux) is not seldom wanting; when present 

 it is supported by a small cylindrical bone, which is attached to 

 the posterior surface of the principal bone of the tarsus. This 

 bone (tarso-metatarsal OWEN) becomes broader at its lower extre- 

 mity and divides into three processes, to which the three anterior 

 toes are attached. The number of joints or phalanges usually 

 increases in birds from the thumb, which has two, to the innermost, 

 middle and outermost, according to the numbers three, four, five; 

 the middle toe, although it has a joint less than the outermost, is 

 generally the longest of all. 



The cranium is connected with the first cervical vertebra (as 

 in the Eeptilia Haplopnoa, p. 255) by an unpaired articular tubercle 

 situated under the large occipital foramen; this occipital foramen 

 is placed lower than in the fishes and reptiles. The internal cavity 

 of the skull is round, and the posterior hollow, for the reception of 

 the cerebellum, is separated from the anterior in which the cere- 

 brum lies; the two occupy entirely the internal cranial space. 

 The bones of the cranium anchylose with each other at an early 

 period; this is less the case, or not at all, with those of the 

 face. In the ostrich, however, the cranial bones remain longer 

 distinct, in which, on that account, they have been especially 

 investigated, as well as in young birds and in the embryo. The 

 occipital bone consists of four pieces; the body, two lateral parts, 

 and the occipital scale. The body of the sphenoid is long, termi- 

 nating in a point forwards, and supports there the bony partition 

 of the orbits, the laminiform ethmoid. On the back part of this 

 body the great alee rest, which are soon anchylosed with it; they 

 form the posterior margin of the orbits, are connected with the 

 temporal and frontal bones, and on the outer surface of the cranium 

 assist in forming a process that is situated behind the orbit. The 

 lesser ala3 continue in part membranous and are situated more 

 upwards, round the large aperture for the passage of the optic 

 nerve. The parietal bones are short and broad; the frontal bones 

 are much larger, and form a considerable part of the upper surface 

 of the skull. When the cranium is viewed on the inferior surface 

 it presents much resemblance with that of the lizards (for instance, 

 with that of the genus Varanus). From the sides of the body of the 



