THE DEVELOPMENT OF THE SKULLS OF FISHES. 



185 



a free styliform process, which lies parallel with, and is bound by 

 connective tissue to, the free hinder cms of an inverted arch of 

 cartilage, the anterior cms of which passes into the pre-frontal 

 region of the ethmo-vomerine cartilage. The centre of this 



Fig. 72. — The cartilaginous and partially ossified crania of young Sticklebacks (Gaster- 

 osteus). — A, in a very early, B, in a more advanced condition, from above ; C, 

 viewed from the side; Ch., notochord ; Au., auditory capsules; P, pituitary fossa; 

 Tr, trabecular ; x. parasphenoid ; H.M., Sy. f Qu., indicate not only the bones, but 

 the pre-existing cartilages. 



palato-quadrate arch is prolonged into a process {Qu.), which 

 articulates with the cartilaginous ramus of the mandible, while 

 the upper part of the cartilage (HM. Sy.) gives attachment to 

 the cartilaginous hyoid {Hy.). 



This is the earliest condition of the cartilaginous cranium of 

 the osseous fish that has yet been observed ; but it can hardly 

 be doubted that the hyomandibular and palato-quadrate carti- 

 lages have already deviated considerably from their primitive 

 condition, and it would be a matter of great interest to ascertain 

 whether these cartilages are primitively continuous ; or whether, 



