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, 

 Qu, M). 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 (suspensorium) for 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 THE SUSPENSORIAL APPARATUS IN 

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

 ELASMOBRANCHS ; C, TORPEDO ; D, TELEOSTBANS ; E, AMPHIBIANS, REPTILES, 

 AND BIRDS ; F, MAMMALS. 



M, Meckel'a cartilage ; PQ, palate-quadrate ; Hm, hyomandibular ; hy, hyoid 

 arch ; Sy, symplectic ; Q (in DandE), quadrate ; Q (in F), articular (malleus), 

 and Q\ quadrate (incus), both of which lie in the tympanic cavity (P) '; h l , 

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

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

 cornu, and c, 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 t 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. 



c. 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 



^ l 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 hyoid arches each represents two. 



