THE SKULL. 



589 



The quadrate cartilage ossifies as the quadrate bone, and 

 supplies the permanent articulation for the lower jaw. Its upper 

 end exhibits a tendency to divide into two processes, corres- 

 ponding with the pedicle and otic processes of the Amphibia. 

 The Meckelian cartilage becomes soon covered by investing 

 bones, and its proximal end ossifies as the articulare. The 

 remainder of the cartilage usually disappears. 



Mammalia. The most extraordinary metamorphosis of the 

 hyoid and mandibular arches occurs in the Mammalia, and has 

 been in part known since the publication of the memoir of 

 Reichert (No. 461). 



Both the hyoid and mandibular arches develop at first more 

 completely than in any of the other types above Fishes; and are 



th-h 



pa.ch nc 



FIG. 341. EMBRYO PIG, TWO-THIRDS OF AN INCH LONG ; ELEMENTS OF THE 



SKULL SEEN SOMEWHAT DIAGRAMMATICALLY FROM BELOW. (From Parker.) 



pa.ch. parachordal cartilage; nc. notochord; . auditory capsule; py. pituitary 

 body; tr. trabeculce; c.tr. trabecular cornu ; pn. prenasal cartilage; e.n. external 

 nasal opening; ol. nasal capsule; p-pg- palatopterygoid tract enclosed in the 

 maxillopalatine process ; tun. mandibular arch; hy. hyoid arch ; th.h. first branchial 

 arch; -ja. facial nerve; 8a. glossopharyngeal ; 8l>. vagus; 9. hypoglossal. 



articulated to each other above, while the pterygo-palatine bar 

 is quite distinct. The main features of the subsequent develop- 

 ment are undisputed, with the exception of that of the upper end 

 of the hyoid, which is still controverted. The following is Parker's 

 (No. 4-52) account for the Pig, which confirms in the main the 

 view originally put forward by Huxley (No. 445). 



The mandibular and hyoid arches are at first very similar 



