GANOCEPHALA 173 



as the produced spines from both neural and hsemal arches 

 bespeak the provision made for muscular attachments, and 

 the vertical development of the caudal swimming organ. 



The skull of the A rchegosaurus appears to have retained 

 much of its primary cartilage internally, and ossification to 

 have been chiefly active at the surface ; where, as in the com- 

 bined dermo-neural ossifications of the skull in the sturgeons 

 and salamandroid fishes — e.g., Polyptcrus, Amia, Lepidosteus — 

 these ossifications have started from centres more numerous 

 than those of the true vertebral system in the skull of saurian 

 reptiles. This gives the character of the present extinct order 

 of Batrackia. 



The skull is much flattened or depressed, triangular, with 

 rounded angles, and the front one more or less produced 

 according to the species ; and in some species according to 

 the age of the individual. The base is concave ; the sides 

 nearly straight, or slightly concave. The basi-occipital appears 

 to have retained its primordial soft, unossified state. Of the 

 ex-occipitals, in a distinctly ossified state, no clear view has 

 yet been had. The super-occipital (fig. 65, 4), is represented, 

 as in the salamandroid fishes, by a pair of flat bones, more 

 probably developed in the epicranial membrane and integu- 

 ment than hi the cartilaginous protocranium. The pair of bones 

 external to these, and forming the prominent angles of the 

 occipital region, represent the " par-occipitals." The lower 

 peripheral surface of the basi-sphenoidal cartilage is ossified 

 with a concave border towards the notochord behind, to the 

 capsule of which it seems to have been attached. The ali- 

 sphenoids were doubtless cartilaginous, and the protocranium 

 there unaltered, as it was apparently in the ex-occipital region. 

 The peripheral ossifications above representing the " parietal" 

 (7), form a pair of oblong flat bones, with the "foramen 

 parietale " in the mid-suture. External to these, and wedged 

 between the parietals, the super- and par-occipitals, are 



