ON THE THEORY OF THE VERTEBRATE SKULL 567 



of the arch, it is true, is not divided into two parts, but nevertheless 

 it represents the whole suspensorium of the iish, and not merely 

 the quadratum of the abranchiate vertebrate, because immediately 

 behind the orbitar process it presents an excavated surface, which- 

 ■articulates with the proximal end of the cornu of the hyoid. That 

 part of the cartilaginous arch, therefore, which lies above and behind 

 this point, corresponds with the proximal division of the suspensorium 

 in the fish, or with the hyomandibular bone; while that portion which 

 hes below and in front of it, corresponds with the distal division of 

 the suspensorium and the anterior crus of the arch in the fish, or in 

 other words, with the symplectic, quadratum, metapterygoid, pterygoid, 

 transverse, and palatine bones. 



In the course of development, in fact, the palatine bone appears, 

 as in the fish, in that part of the arch which is immediately con- 

 nected with the ethmo-presphenoidal cartilage, and a single pterygoid 

 in that part of its anterior crus which lies between the palatine and 

 the articular portion, which obviously represents the quadratum. 

 But this pterygoid is, in the adult frog, a large bone, which, on the 

 one hand, stretches down on the inner side of the quadrate cartilage, 

 and, on the other, sends a process inwards and upwards, which 

 nearly reaches the base of the skull. If the pterygoid, transverse, 

 and metapterygoid of the fish were anchylosed into one bone, or if 

 the corresponding region of the primitive cartilage were continuously 

 ossified, the result would be a bone perfectly similar to the pterygoid 

 of the frog ; and I entertain no doubt that the amphibian pterygoid 

 does really represent these bones. 



The inferior ossification in the batrachian suspensorium certainly 

 answers to the quadratum, in Triton — whether it should be regarded 

 partly or wholly as a quadrato-jugale in the frog seems to be a 

 ■question of no great moment — inasmuch as we may be quite sure 

 that the lower end of the frog's suspensorium represents the quadrate 

 or incudal element in other Vertebrata. 



It is well known that, in the course of the development of the frog, 

 the end of the suspensorium, as it were, travels backwards, so that 

 its axis, instead of forming an acute angle, open forwards, with that 

 of the cranium, as in the tadpole (fig. 9), forms a very obtuse angle, 

 open downwards, in the adult frog. This change is accompanied by a 

 relative and absolute lengthening of that part of the suspensorium 

 which lies between the articulation of the hyoid and that of Meckel's 

 cartilage (containing its proper quadrate portion), and by a relative 

 shortening of that part which lies between the articulation of the 

 hyoid and the skull (or the hyomandibular portion). The conse- 



