XI.] PROBOSCIDEA. 203 



by Brandt as articulating with the mastoid process of the 

 skull, represents the stylohyal. 1 



PROBOSCIDEA. The skull of the only existing animals of 

 this group, the Elephants, presents many very remarkable 

 features. As the brain-case increases but little in size 

 during growth, and as the exterior wall of the skull is required 

 to be of great superficial extent to support the trunk and the 

 huge and ponderous incisor teeth or rusks, and to afford 

 space for the attachment of muscles of sufficient size and 

 strength to wield the skull thus heavily weighted, an extra- 

 ordinary development of air-cells takes place in the can- 

 cellous tissue between the outer and inner surface walls or 

 " tables " of nearly all the bones of the cranium, separating 

 them in some cases as much as twelve inches apart (see 

 Fig. 64). These cells are not only formed in the walls of the 

 cranium proper, but are also largely developed in the nasal 

 bone and upper part of the premaxilla and maxilla, the bones 

 forming the palate and the basicranial axis, and even 

 extend into the interior of the ossified mesethmoid and 

 the vomer. Where two originally distinct bones come in 

 contact the cells pass freely from one to the other, and 

 almost all the sutures become completely obliterated in old 

 animals. 



The intercellular lamellae in the great mass which sur- 

 rounds the brain-cavity superiorly and laterally mostly 

 radiate from the inner to the outer table, but in the other 

 bones their direction is more irregular. Like the similar but 

 less developed air-cells in the skulls of many other Mammals, 

 they are entirely secondary to the original growth of the 

 bones. In the young African Elephant's skull figured (from 



1 "Mem. de 1'Acad. Imp. de St.-Petersbourg," Vile Serie, tomexiv. 

 No. 2, p. 68 (1869). 



