IN THE PAEAGUAYAN LEPIDOSIRBN, ETC. 353 



the result of the exceptional forward and downward growth of the dermal ectethmoid 

 in front of the eye. It is also equally clear that the cartilages in question do not 

 precisely agree in position with the upper labials of Lejndosiren, inasmuch as they have 

 no ligamentous connection with the hinder margin of the nasal roof. Considered 

 either as antorbital processes or as labial cartilages, tliere can be no doubt that their 

 position and relations have been greatly modified by the extensive preorbital growth of 

 the dermal ectethmoid, which seems to have dissociated them, as it were, from their 

 primitive relations to the chondrocranium or to the nasal capsules, as Jhe case may be, 

 and in the absence of developmental data it seems impossible to decide as to the real 

 nature of these structures. The anterior upper labials of Huxley have certainly nothing 

 in common with the undoubted upper labials of other Dipnoi, since they lie anteriorly 

 to the posterior nasal aperture, practically, in the floor of the nasal sac between the 

 two narial openings — that is to say, in the position occupied by the inner half of the 

 subnasal cartilage in Lejndosiren ; and if they are rightly to be regarded as upper 

 labials, it is evident that they must represent an additional pair of these structures 

 which have no counterpart in any other Dipnoi. For my own part, I am inclined 

 to believe that these cartilages owe their existence to the dismemberment of a 

 subnasal cartilage, primitively continuous with the outer margin of the cartilaginous 

 nasal roof, and therefore cannot be true labials. There are several facts which seem 

 to be in harmony with this suggestion. In the first place, the so-called anterior labials 

 of Ceratodus and the subnasal cartilages of Lejiidosiren occupy precisely similar positions 

 in the floor of each nasal sac between the anterior and posterior nasal apertures, and 

 both are attached, internally or mesially, to the internasal septum by fibrous tissue. 

 Further, the outer margin of each nasal capsule in Ceratodus gives off a short lateral 

 process (Huxley, I. c. p. 37, fig. 7), which coincides externally with the position of the 

 " anterior labial " internally and ventrally, and may possibly represent the outer portion 

 of a transversely-divided subnasal cartilage. Lastly, the subnasal cartilage of Lejndo- 

 siren is somewhat constricted at one point — a fact which may perhaps be taken to 

 suggest the possibility of its inner portion becoming segmented off' from the rest as an 

 independent cartilage similar to the supposed anterior upper labial of Ceratodus. 



The only endochondrial bones in Ceratodus are the two exoccipitals. They have 

 been correctly described by Huxley as two hollow cones of bone embedded in the side- 

 walls of the skull near its junction with the vertebral column. Each is said to be 

 " wider above and externally than below and internally, where it lies above the 

 notochord " \l. c. p. 38]. I may add that the bones are so thickly invested externally 

 by cartilage as to be completely hidden in a lateral view of the skull, and for this 

 reason in all probability they escaped the notice of Giinther. 



With the exception of a fronto-parietal bone, which is entirely absent, and the 

 presence of a " scleroparietal " (Giinther, I. c), and also of a series of four or five 



