in.] THE CRANIAL SKELETON. 115 



The second element of the human maxillary bone namely, 

 that in which the incisor teeth are implanted is termed i'n 

 zootomy the pre-maxilla. Its existence in man, even at 

 birth, is obscured (except on the surface of the palate) by 

 anchylosis, and masked by the extension over it of a delicate 

 plate, or lamina, of the first and far larger portion of the 

 maxillary bone. This lamina is wanting in all other animals, 

 and even in the Apes the maxillo-premaxillary suture is for a 

 long time or permanently very evident on the face. 



A pre-maxilla is almost a constant element in an osseous 

 skull; nevertheless, in some Bats and Shrews (e.g. Crocidura) 

 it seems to abort. It may attain a vast size, as in Birds, 

 where it forms the greater part of the upper half of the beak, 

 and reduces the part representing the other element of the 

 human maxillary to insignificance. Generally double in Ba- 

 trachians, apparently always so in Fishes, a single median 

 ossification may nevertheless, as in Serpents, represent the 

 pre-maxillae of both right and left sides conjoined. 



In man's class the pre-maxilla varies greatly in size in dir- 

 ferent animals, and this independently of the development 

 both of the muzzle and of the teeth ; for the Ant-eater and the 

 Whale are both edentulous, and both have an enormously pro- 

 duced muzzle, yet, while in the former the pre-maxilla is ex- 

 tremely small, in the latter it is very largely developed. A 

 nasal spine is very rare, but may exist below man, as in 

 Pedetes and the Walrus. 



Generally the development of the pre-maxilla is related to 

 that of the incisor teeth, which are defined by the fact of their 

 being implanted in it, though when they are very large, as in 

 Rodents, their roots may extend backwards into the parts 

 which represent the first-described element of the maxillary 

 bone of man. 



In some Bats (e.g. Vespertilio noctula], and the Ornitho- 

 rhynchus, we find the pre-maxilla separated by an interval 

 from its fellow of the opposite side. On the contrary, these 

 may be united not only below but also above the anterior 

 nares, as in the Gavial and Echidna. Again, they may be 

 united in the middle line, but altogether separated from the 

 first-described element of the human maxillary bone, as in the 

 Three-toed Sloth and in Serpents. 



In this latter case we have normallv existing that occasional 

 abnormal arrest of development in man, which we call 

 " hare-lip." 



26. The MALAR bone is almost at its maximum of relative 

 I 2 



