TILE SKULL. 



483 



assumed its permanent position on tlie hinder border of the no longer 

 suctorial mouth, and has grown forwards so as nearly to meet ^its 

 fellow in the median line. 



The metapterygoid region of the quadrate gives rise to a posterior 

 and dorsal process (fig. 339, ot^pr), the end of which is constricted off 

 as the tympanic annulus (fig. 340, a.t)\ while the proximal part of 

 the process remains as the 

 otic (metapterygoid) pro- 

 cess, articulating with the 

 auditory cartilage. 



The pedicle {^d) retains 

 its orginal attachment to 

 the skull. 



The palato-pterygoid 

 soon becomes segmented 

 into a transversely placed 

 palatine, and a longitudi- 

 nally placed pterygoid (fig. 

 340). With the exception 

 of a few ossifications, which 

 present no features of 

 special interest, the parts 

 of the mandibular arch 

 have now reached their 

 final condition, which is 

 not very different from that 

 in the Axolotl. 



Sauropsida. In the 

 Sauropsida the modifica- 

 tions of the hyoid and 

 mandibular arches are 

 fairly uniform. 



The lower part of the 

 hyoid arch, including the 

 basihyoid, unites with the 



remnants of the arches behind to form the hyoid bone, to which it 

 contributes the anterior cornu and anterior part of the body. 



The columella is believed by Huxley and Parker to represent, 

 as in the Anura, the independently developed dorsal (hyoraandibular) 

 element of the hyoid, together with the stapes with which it has 

 become united'. 



Fig. 340. Young Frog, near end of first 

 summer ; upper view of skull, with left man- 

 dible removed, and the right extended outwards. 

 (From Parker. ) 



h.o. basioccipital tract ; s.o. supraoccipital 

 tract ; Jo. frontal fontanelle ; e.n. external nostril ; 

 internal to it, internasal plate ; a.t. tympanic 

 annulus. 



Bones: e.o. exoccipital; i^r.o. prootic, partly 

 overlapped by p. parietal ; /. frontal ; eth. rudi- 

 ment of sphenethmoid ; na. nasal ; 'pmx. premax- 

 illary ; inx. maxillary ; ■pg. pterygoid, partly en- 

 sheathing the reduced cartilage ; q.j. quadratojugal ; 

 sq. squamosal; ar. articular; d. dentary; m.vik. 

 mento-Meckelian. 



^ The strongest evidence in favour of Huxley's and Parker's view of the nature of 

 the columella is the fusion in the adult Sphenodon of the upper end of the hyoid with 

 the columella (vide Huxley, No. 445). From an examination of a specimen in the 

 Cambridge museum I do not feel satisfied that the fusion is not secondary, but have 

 not been able to examine the junction of the hyoid and columella in section. For a 

 different view to that of Huxley vide Peters, "Ueb. d. Gehorknochelchen u. ihr 

 Verhaltniss zu. Zungenbeinbogen b. Sphenodon." Berlin Monatuberichte, 1874. 



31—2 



