IN THE PARAGUAYAN LEPIDOSIEEN, ETC. 341 



internasal septum, the two capsules are entirely devoid of any cartilaginous floor. 

 These rods may be termed the subnasal cartilages. 



The most noteworthy feature in connection with the olfactory region of the skull of 

 Lepidosiren is the effect produced on the chondrocranial elements by the relatively 

 massive development of the palatine symphysis. Not only has the dorsal growth of the 

 symphysis completely interrupted the direct continuity of the internasal septum and 

 mesethmoid cartilage, so that the symphysial portions of the palatines (PL XXVIII. 

 fig. 4, and PI. XXIX. fig. 12, ]).sy.) are in actual contact with the hinder part of the 

 nasal roof in the median line (fig. 12), but, by its extension anteriorly and mesially 

 between the two nasal sacs for nearly two-thirds of their extent, the symphysis, and not 

 the true internasal septum, forms the actual median division between the two capsules. 

 Eeference to fig. 12 will sufficiently illustrate these modifications and also show how, in 

 consequence of its forward extension, the symphysis reduces the vertical dimension 

 of each capsule, while at the same time contributing to the support of the nasal 

 floor. 



As will be shown later on, the accounts given by different writers as to the existence 

 of upper labial cartilages in the Dipnoi are not always easy to reconcile one with 

 another or with actual facts, and not infrequently they are mutually contradictory. 



In Lepidosiren the structures erroneously regarded as labial cartilages by Bischoff 

 and Hyrtl are without doubt antorbital cartilages, formed as lateral outgrowths from 

 the anterior trabecular region of the chondrocranium, between the orbital and nasal 

 regions, and, as already mentioned, may be considered as the equivalents of similarly- 

 situated cartilages in the Elasmobranchs and Urodele Amphibians. The true upper 

 labials were overlooked by both of these writers, but there can be no question as to 

 their existence. Attached by ligament to the posterior margin of each nasal capsule, 

 near its junction with the internasal septum, there is a slender cartilaginous filament 

 which passes directly downward, immediately anterior to the initial descending portion 

 of the antorbital process, and ends in the fibrous posterior wall of the nasal capsule 

 (PI. XXVIII. figs. 1, 3, and 5, u.l.c). These filaments represent a single pa^r of upper 

 labial cartilages, and are the only structures which can be recognized as such in 

 Lepidosiren. 



The anterior section of the cranial cavity for a short distance behind the mesethmoid 

 cartilage is completely filled by a dense mass of extremely tough fibrous tissue, con- 

 tinuous dorsally with the fibrous connection between the dermal ethmoid and the 

 fronto-parietal, and also filling up the two olfactory passages. The hinder face of 

 this fibrous plug is slightly hollowed out for the reception of the anterior extremity 

 of the brain. The mass is also traversed by the two Olfactory nerves as they pass 

 forward to enter the two olfactory passages, and into it projects the median styliform 

 process from the mesethmoid cartilage (PI. XXIX. fig. 14). 



The lower jaw of Lepidosiren is very similar to that of Protopterus, as described by 

 VOL. XIV. — PARI V, No. 3. — Fehiuary, 1898. 2 x 



