411 



Nevertheless, in their very earliest conditions, these embryos are 

 said to present a structure, which, if I mistake not, shadows forth the 

 organization of the fish. The visceral arches, in which the man- 

 dibular and hyoid cartilages are developed, are at first separated to 

 the very base of the cranium by a deep cleft, the anterior visceral 

 cleft, so that the semi-cartilaginous rudiments of the mandibular 

 and hyoid are completely separate. Subsequently they are said to 

 coalesce above, as the visceral cleft diminishes, so as to have a com- 

 mon root of attachment to the cranium ; and this, I apprehend, 

 answers to the hyomandibular bone, and its prolongation to the 

 symplectic. With advancing development, however, this part does 

 not advance, but remains stationary, and becomes confounded with 

 the wall of the cranium ; so that the two arches subsequently appear 

 to be attached to the latter quite independently, and there is nothing 

 left to represent this division of the suspensorium in fishes. 



I am strengthened in this view by the structure and develop- 

 ment of the palatosuspensorial apparatus in the Amphibia, whose 

 consideration I deferred when speaking of the skull in that class. 

 On examining a young tadpole (fig. 9), a cartilaginous process is seen 

 to arise from the walls of the cranium, opposite the anterior part of 

 the auditory capsule, and, passing obliquely downwards and forwards, 

 to end in a rounded condyloid head, which articulates with the repre- 

 sentative of Meckel's cartilage. At the anterior boundary of the 

 orbit the process gives off a broad, nearly vertical apophysis (O), which 

 ends superiorly in a free, rounded, and incurved edge. The crota- 

 phite muscle passes to its insertion on the inner side of this, the 

 so-called "orbitar process." From the condyle the cartilaginous 

 process sweeps upwards and inwards, and ends by passing into the 

 ethmo-presphenoidal cartilage. It consequently forms an inverted 

 arch, whose keystone is the condyle for Meckel's cartilage, and is, in its 

 connexions and form, strictly comparable with the cartilaginous arch 

 which I have described in the embryo fish. The posterior crus of 

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

 it represents the whole suspensorium of the fish, 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 



