in.] THE CRANIAL SKELETON. 1O3 



margins of the glenoid surface are so prolonged that the 

 lower jaw cannot be removed, even from the dry skull with- 

 out fracture of one of those osseous processes. 



FIG. loo. SIDE VIEW OF THE SKULL OF A PERCH. (After Citvier.) 

 i, the frontal ; 2, the pre-frontal ; 4, the sphenotic ; 7, parietal ; 8, supra-occipital ; 

 9, exiotic; ir, pro-otic ; 12, pterotic ; 17, pre-maxilla ; 18, maxilla; 19, 

 first sub-orbital bone, or lachrymal ; 19', chain of posterior sub-orbitals ; 20, 

 nasal ; 21, one of a chain of post-temporal ossicles ; 23, hyo-mandibular ; 24, 

 ecto-pterygoid ; 26, quadrate ; 27, meta-pterygoid ; 28, operculum ; 30, pre- 

 operculum ; 31, symplectic ; 32, sub-operculum ; 33, inter-opcrculum ; 34, 

 dentary ; 35, articular ; 36, angular ; 42, urohyal ; 46, post-temporal, or bone 

 connecting scapular arch with skull. 



The projecting (zygomatic) portion of the squamous element 

 is constantly present in Mammals, though it may end freely, 

 as in Centetes- and Sorex, or join the frontal instead of the 

 malar, as in the Horse. 



It also projects freely downwards in most Birds, but 

 it may (as in some Parrots) articulate with a post-frontal 

 element. 



In Reptiles also it may project forward, and form a sort of 

 upper zygoma by articulating with the post-frontal, as in some 

 Lizards (e.g. Sphenodon, Cyclodm\ or it may be articulated 

 with the cranium at one end only, as in Python the other 

 end projecting backwards and slightly outwards, to give ad- 

 ditional mobility to the lower jaw. 



