THE SKULL. 



61 



which the uppermost becomes inserted under the base of the 

 skull, while the lowermost comes to lie ventrally, and is connected 

 with 'its fellow by a median piece, or basi-branchial (Fig. 45, 1 



to 4, Cp). 



The two anterior visceral arches also undergo a segmentation. 

 Thus the first becomes divided into a short proximal piece, the 

 quadrate, and into a long distal Meckel's cartilage (Fig. 46, 



;./). The quadrate grows out anteriorly into a process, the 

 palatoquadrate or palatopterygoid (Figs. 47 and 48, A to C, 

 PQ), which becomes fixed to the base of the skull, and thus forms a 

 sort of primary upper jaw. 



The quadrate, which serves as a support ^suspensonum) tor the 

 lower jaw, either remains separated from the skull by an articu- 

 lation, that is, is only united to it by connective-tissue, or it forms 

 one mass with it. 



The hyoid arch, which always stands in close relations to the 

 mandibular, and may also take part in its suspensorial apparatus, 1 



FIG. 48. SEMI-DIAGRAMMATIC FIGURES OF TITE SUSPEXSORIAL APPARATUS IN- 

 VARIOUS VERTEBRATES. (Mainly after Gegenbaur.) A, XOTIDAXUS ; B, OTHER 

 ELASMOBRAXCHS ; C, TORPEDO ;" D, TELEOSTEAXS ; E, AMPHIBIANS, REPTILES, 

 AKD BIRDS ; F, MAMMALS. 



M, Meckel's cartilage ; PQ, palato-quadrate ; Hm, hyomandibnlar ; hy, hyoid 

 arch ; Sy, symplectic ; Q (in D and E), quadrate ; Q (in F), articular (malleus), 

 and Q 1 , quadrate (incus), both of which lie in the tympanic cavity (P) ; A 1 , 

 styloid process, connected with the anterior (lesser) corner of the hyoil (h) by 

 the stylohyoid ligament, indicated by the dotted lines ; b, the posterior (greater) 

 cornu, ande, the body of the hyoid in Mammals. 



becomes divided, as do the true branchial arches, into a great 

 number of pieces (Fishes), which are distinguished from above 

 downwards as hyomandibular, symplectic, and hyoid in a 

 narrower sense (Fig. 48, A to D, Em, Sy, hy). In the mid-ventral 

 line there is a basi- hyal connecting the arch of each side, and this 

 becomes ossified, and is embedded in the tongue as the entoglossal 

 or glossohyal. 



. The Bones of the Skull. 



Two kinds of bone, genetically distinct, may be distinguished, 

 one arising within cartilage, the other in connective-tissue, in those 



1 According to Dohrn, Meckel's cartilage and the palatopterygoid are separate in 

 origin, as are also the hyomandibular and hyoid proper, and thus the so-called 

 mandibular and hycid arches each represents two. 



