588 MAND1BULAR AND IIYOID BARS. 



The palato-pterygoid soon becomes segmented into a trans- 

 versely placed palatine, and a longitudinally placed pterygoid 

 (fig. 340). With the exception of a few ossifications, which pre- 

 sent 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 modifications 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 (hyoman- 

 dibular) element of the hyoid, together with the stapes with which 

 it has become united 1 . 



The membranous mandibular arch gives off in the embryos 

 of all the Sauropsida an obvious bud to form the superior 

 maxillary process, and the formation of this bud appears to 

 represent the growth forwards of the pterygoid process in Elas- 

 mobranchii, which is indeed accompanied by the formation of a 

 similar bud ; but the skeletal rod, which appears in the axis 

 of this bud, is as a rule independent of that in the true arch 

 (fig- SS 1 ./^. PS}- The former is the pterygo-palatine bar; the 

 latter the Meckelian and quadrate cartilages. 



The pterygo-palatine bar is usually if not always ossified 

 directly, without the intervention of cartilage. 



Born has recently shewn that Parker was mistaken in supposing that 

 the palato-pterygoid bone is cartilaginous in Birds. In the Turtle a short 

 cartilaginous pterygoid process of the quadrate would seem to be present 

 (Parker, No. 458). 



The quadrate and Meckelian cartilages are either from the 

 first separate, or very early become so. 



1 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 MoHOtsbtnekU, 1874. 



