340 PROF. T. W. BRIDGE ON THE MORPHOLOGY OE THE SKULL 



below with the basicranial cartilage, becomes continuous in the median line with the 

 cartilaoe of the nasal roof. The tubular passage on each side of the mesethmoid cartilage 

 is limited externally by the ascending process of the palato-pterygoid, and not, as in 

 Ceratodus, by an extension of the lateral wall of the chondrocranium, and communi- 

 cates anteriorly with the nasal sac of its side dorsad to the palatine symphysis. 



The internasal septum (PL XXVIII. fig. 4, and PL XXIX. fig. 11, i.n.s.) begins as 

 an inconspicuous inwardly-projecting ridge from the median line of the cartilaginous 

 nasal roof, but is separated from the mesethmoid cartilage by a deep arch-like notch 

 (fig. 4) resulting from the upward growth of the palatine symphysis. Anteriorly to the 

 symphysis the septum increases in vertical extent and also thickens somewhat, 

 supporting on its ventral margin the two acutely-conical vomerine teeth (PI. XXVIII. 

 figs. 3 and 4 ; PI. XXIX. fig. 11, vo.t.). In front of the anterior boundary of the nasal 

 capsules the internasal septum projects into the upper lip in the form of a short 

 prenasal process terminating in two short laterally-directed cornua (PL XXVIII. 

 figs. 2, 3, and h,pn.p.). Laterally, the septum is prolonged outward into two thin 

 laminse of cartilage with deflected and slightly thickened external margins, which form 

 the roof and outer walls of the dorsally-convex and ventrally-concave nasal capsules 

 (PL XXVIII. figs. 1, 2, and 5, n.c.). Dorsally, the internasal septum, and to some 

 extent also the roof of each capsule, are invested by the dermal ethmoid (fig. 2). 



As in Ceratodus and Protopterus, the continuity' of each nasal roof is interrupted by 

 a series of vacuities which in Lepidosiren are elongated and somewhat oval in shape, 

 transversely disposed, and in the fresh specimen filled in by fibrous membrane L At 

 the anterior margin of each nasal capsule the cartilage is somewhat thicker than else- 

 where, and laterally projects outward in the form of a thickened and slightly recurved 

 process (figs. 1, 2, 5, i.e.). From their position, and their relations to the anterior 

 boundary of the nasal capsules, I am inclined to regard these cartilages as representing 

 the persistent trabecular cornua of the embryonic skull ; in any case, they closely 

 resemble the well-known trabecular cornua which Parker [31] has described in such 

 Anurous Amphibia as, for example, Bufo omatus. By Rose [36], on the contrary, the 

 equivalent cartilages in Protopterus are regarded as representing a pair of " upper 

 labials," but on what grounds it is difficult to see. With the exception of a thin 

 rod of cartilage (PL XXVIII. figs. 3 and 12, sn.p.), which extends inward from 

 the deflected outer margin of each nasal capsule and passes between the ventrally- 

 situated anterior and posterior narial apertures to a fibrous attachment to the 



With the exception of the Dipnoi, this curious fenestration of the nasal roof occurs in no other Vertebrates 

 except certain Urodele Amphibia [Wiedersheim 43, H. H. Wilder 44], and affords another instance of the 

 many homoplastic modifications which are to be noticed in the two groups. 



[Since the above footnote was written, I have been informed by Professor Howes that the nasal capsules of 

 a skull of Cestracion philijapi, in the Museum of the Royal College of Science at South Kensington, exhibit 

 feeble, but nevertheless unmistakable, indications of fenestration.] 



