1 1 6 ELEMENTAR Y ANA TO MY. [LESS. 



development in man, and only in Mammals and the Crocodile 

 does it approximate to the condition it attains in him. It is 

 a less constant bone than the maxillary, as it is absent in 

 some Mammals, e.g. Centetes and Mams, also in Batrachians, 

 Serpents, and generally in Fishes. 



It may be merely a delicate spiculum of bone, helping to 

 form the zygoma, as is the case in Birds. 



In none but man and Apes does the malar develop the 

 orbital plate, and generally in Mammals it does not even 

 meet the frontal outside the orbit ; and when the orbit is 

 encircled by bone, the malar may be separated from the 

 frontal by the intervention of the zygomatic process of the 

 temporal bone, as in the Horse. 



Processes may be developed which do not exist in man, as 

 is the case in the Sloths, where there is both an ascending 

 and a descending process, but no process to form a junction 

 with the zygomatic portion of the temporal bone. 



There may be a considerable perforation in the malar, as 

 in some Lemurs and Insectivora. 



Sometimes, as in the Porpoise, the malar may be double 

 the zygomatic portion being a separate ossification from its 

 front part. 



27. The NASAL bones are more constant elements of the 

 bony skull than are the malar bones, as, except in most 

 Chelonians, they seem to be constantly developed. There 

 may be a pair of them, as in man (and this is the general 

 rule), or there may be but a single median ossification, as is 

 the case in Varanian Lizards. Even in man's class (Mammalia) 

 they may be represented by a single bone through their early 

 anchylosis, as is the case in Centetes, Spalax, and the Orang. 



The very extremes of development of these bones are also 

 to be found in the same class, as in the last-mentioned form 

 (the Orang) they all but abort, and in the Porpoises they form 

 small rounded masses, each lying in a concavity on the 

 frontal bone, and not at all roofing over the nasal passages. 

 On the other hand, in the Porcupine they are of enormous 

 size, in fact the largest of the cranial bones. 



In the Porpoises the two nasals may cease to follow the 

 general rule among Mammals, of joining each other. In 

 Fishes they may lie wide apart. They may be shut out from 

 bounding any part of the anterior nares, as in the Chameleon, 

 where the pre-frontal extends to the maxilla, as before 

 mentioned. 



28. The LACHRYMALS may be altogether absent, or may 



