668 H. H. SWINNERTON. 



between tbe cranium of a lamprey and that of a Teleost is 

 a close relation between the epiphysis and the sphenoidal 

 " tegmen/^ which would then be the undoubted homologne 

 of the epiphysial cartilage. Failing- this, it will suffice to 

 recall tbe fact that in the Cyprinoids and Characinoids this 

 cartilage also arises directly from the sphenoidal region. 



Parker himself considered that other types of fish, especially 

 Lepidosteus, were descendants of primordial Marsipobranchs 

 (83, p. 404), and the facts jnst put forward lend considerable 

 support to this. 



The possibility, of course, still remains that between this 

 " primordial Marsipobrauch '' and the bony fish a form like a 

 cartilaginous Ganoid, having bony scutes, as well as a box-like 

 cartilaginous cranium, may have intervened ; and that as the 

 scutes became more closely related to this, the fontanelles 

 present in the embryo were preserved, and the necessity for 

 further growth in cartilage was obviated. It is equally 

 possible that on the bony fish side bony specialisation 

 appeared earlier, and was more rapid than in the Chondrostei, 

 and resulted in a preservation of the fontanelles (with the 

 possible exception of the roof) all through. 



Again, the fontanelles always present during development 

 might conceivably be explained as due to the relatively large 

 size of the brain ; but such an explanation would not apply 

 to the condition of the Marsipobrauch cranium. 



The Relation of the Visceral Skeleton to the 

 Cranium. 



Great interest attaches to a study of the relationships of 

 the so-called liyoid and mandibular arches, and such a study 

 may best be commenced by briefly comparing the conditions 

 found in the adult Heptanchus, as a primitive Selachian, and 

 Gasterosteus, as a typical Teleost. 



In the latter the hyomandibular articulates on the auditory 

 capsule below and behind the post-orbital process, and the 

 palatine process of the pterygo-quadrate articulates with the 

 side of the ethmoid plate. 



