72 FISHES. 



Neural and haemal elements and ribs are well developed. 

 In Ceratodus each neurapophysis consists of a basal cartiLa- 

 ginoTis portion, forming an arch over the myelon, and of a 

 superadded second portion. The latter is separated from the 

 former Ify'a distinct line of demarcation, and its two branches 

 are more styliform, cartilaginous at the ends and in the centre, 

 but with an osseous sheath, and coalesced at the top, forming 

 a gable over an elastic iibrous band which runs along and 

 parallel to the longitudinal axis of the column {Ligamentum 

 longitudinale superius). To the top of this gable is joined a 

 single long cylindrical neural spine. Prom the eleventh 

 apophyseal segment a distinct interneural spine, of the same 

 structure as the neural, begins to be developed, and farther on 

 a second interneural is superadded. Towards the extremity 

 of the column these various pieces are gradually reduced in 

 size and number, finally only a low cartilaginous band (the 

 rudiments of the neurapophysis) remaining. The hcemapophy- 

 ses are in form, size, and structure, very similar to the neura- 

 pophyses ; and all these long bones, including the ribs, have 

 that in common, that they consist of a solid rod of cartilage 

 enclosed in a bony sheath, which, after the disappearance or 

 decomposition of the cartilage, appears as a hoUow tube. 

 Such bones are extremely common throughout the order of 

 Ganoids, and their remains have led to the designation 

 of a family as Gcdacanthi (koi\o<;, hollow; and aKavdo<;, 

 spiae). 



The primordial cranium of the Dipnoi is cartilaginous, 

 but with more or less extensive ossifications in its occipital, 

 basal, or lateral portions, and with large tegumentary bones, 

 the arrangement of which varies in the different genera. 

 There is no separate suspensorium for the lower jaw. 

 A strong process descends from the cranial cartilage, and 

 offers by means of a double condyle (Fig. 35 s) attach- 

 ment to corresponding articulary surfaces of the lower jaw. 



