SKELETON OF THE COMMON PIGEON. 63 



at the anterior end of the rostrum. The internal nares open between the rostrum 

 and the palatines, and there is no hard palate. The Pigeon, like many birds, 

 is in a permanent state of cleft palate (schizognathism), owing to the palatal plates 

 of the praemaxilla and maxilla not meeting in the middle line. 



The lower jaw of the young Fowl has five bones in each ramus, a dentary, 

 splenial, angular and surangular with one cartilage bone, the articular. Some Birds 

 add a coronoid, thus attaining the standard of the Lacertilian. The symphysis in 

 the Cretaceous toothed birds was ligamentous. 



The hyoid is characteristic. There are three median bones, one tongue- 

 shaped, formed by the union of the ceratohyals, followed by the basihyal and a 

 basibranchial. The first branchial arch is well developed, and consists of an 

 upper epi- and a lower cerato-branchial. The joints between the several parts are 

 synovial. 



Archaeopteryx (Jurassic), Ichthyornis and Apatornis (Cretaceous) had amphi- 

 caelous vertebrae like the Geckoes and Hatteria among living Lizards. The third 

 cervical of Ichthyornis shows transitional characters to the modern Bird, and closely 

 resembles the corresponding vertebrae in the Tern (Marsh). A transitory amphi- 

 caelous stage exists in the chick on the seventh day. Some of the dorsals in the 

 Penguin, Auks, Plovers have spheroidal faces and are opisthocaelous. The cervical 

 ribs remain distinct for a long time in Ratitae. The division between cervical and 

 dorsal vertebrae is somewhat arbitrary. The late Professor Rolleston considered 

 the two vertebrae with ribs not touching the sternum as dorsals, because the ribs 

 indent the lungs, and the last pair carries uncinate processes. Professor Huxley 

 considers them as cervicals because the ribs do not touch the sternum. But there 

 is embryological evidence in favour of the former view. It has been shown by 

 Miss B. Lindsay that two anterior ribs in the Fowl and one in the Gannet are 

 continuous at an early stage with the sternum, but become separated from it 

 subsequently by atrophy. The identification of two vertebrae as ' sacral ' and as 

 homologous with the vertebrae so named in Lizards depends on the following 

 points : (i) their predominant size in the embryo ; (2) the presence of free ribs 

 ossifying by separate centres in the embryo while the preceding vertebrae are devoid 

 of them ; (3) that these ribs expand and fuse distally, as in the Crocodile ; (4) that 

 they are in relation with the acetabulum ; and (5) that the nerve passing out 

 between the ribs is the last and weakest factor in the plexus ischiadicus, as in 

 Lizards. 



Anchylosis of three dorsal vertebrae is characteristic of the Peristeromorphae 

 (Pigeon group), while four are similarly anchylosed in the Alectoromorphae (Fowl 

 group), but the first is a cervical. 



Archaeopteryx has but five anchylosed sacral vertebrae, and the tail contains 

 twenty vertebrae, of which the last fifteen are devoid of transverse processes, and 

 carry each a pair of large feathers. Hesperornis has fourteen sacral and twelve 

 caudal vertebrae, of which the last six or seven are anchylosed by their centra only, 

 and are in other respects free. 



The sternum is formed from right and left plates of cartilage, constituted by 

 the fusion of the ventral ends of the ribs. The absence "of transverse segmentation 

 universal in Mammalia is characteristic of Birds and Reptiles. The carina, 

 according to Gotte and Hoffmann, is formed from a single or primitively double 



