IN THE PARAGUAYAN LEPIDOSIREN, ETC. 335 



of the two bones is doubtlessly associated with their function as basal supports for the 

 powerful palatal teeth, but the effect produced on the nasal region of the skull is 

 remarkable, and will be referred to subsequently. As described by Wiedersheim in 

 Protopterus, the symphysial extremity of each bone is produced into three processes 

 which, when viewed ventrally (fig. 3), appear to radiate outward from the median line 

 of the symphysis. Of these processes, the hinclermost and strongest is nearly transverse, 

 or at most has but a slight backward inclination, and, projecting outward, terminates in 

 a pointed extremity (figs. 1-3 and 13, at. p.). This is the equivalent of the "Processus 

 antorbitalis " of Wiedersheim, and, in conjunction with the body of the bone, supports 

 ventrally the basal portion of the posterior and largest of the three plate-like palatine 

 teeth (fig. 3,p>.p.t.). The central process is transversely disposed and supports the 

 much smaller central tooth (m.p.t.), while the third is directed obliquely outward and 

 forward, and forms the basis of the anterior and smallest of the palatal teeth (a.p.t.). 

 In addition to the three tooth-supporting processes, the anterior portion of each palato- 

 pterygoid gives off from its dorsal border a stout conical process, corresponding to 

 the " Processus ascendens " of Wiedersheim, which is directed obliquely upward and 

 backward, and terminates in a pointed extremity projecting a little beyond the level 

 of the cranial roof (figs. 1 and 5, p.pt.a.). The process extends so far backward 

 as to overlap the anterior margin of the fronto-parietal (fig. 1), and fill up what would 

 otherwise be an oblique notch or fissure between the lateral, or descending, and the 

 dorsal portions of that bone, and therefore, as seen in figs. 4 and 13, contributes to 

 the formation of the outer wall of the extreme anterior section of the cranial cavity 

 and of the olfactory fossa of its side. Dorsally, the two processes are separated from each 

 other by the anterior extremity of the fronto-parietal (figs. 2 and 5), and each is over- 

 lapped, and partially hidden from view, by the expanded anterior section of the dermal 

 ectethmoid. On the outer surface of each process there is a strong lateral ridge, 

 coincident in direction with the inclination of the process itself, but terminating above 

 in a free projecting extremity, which is clipped by the bifurcate outer margin of 

 the anterior extremity of the ectethmoid (figs. 1, 2, 5, and 13, p.pt.a'.). 



The squamosal bone ("Quadrate," Bischoff and Hyrtl; in Protopterus, the " Quadrate," 

 Peters, " tympanic," Owen, " zygomatic" or " jugal," Cobbold, " squamosal," Huxley and 

 Wiedersheim ; in Ceratodus, the " squamosal" of Giinther and Huxley) invests the outer 

 surface of the hinder part of the suspensorial cartilage (PI. XXVIII. figs. 1 and 2 ; 

 PI. XXIX. figs. 17 and 18, sq.). For the dorsal two-thirds of its extent it is a relatively 

 thin plate, somewhat ovate in shape, its posterior margin coinciding with the hinder 

 edge of the suspensorial cartilage (fig. 1). Interiorly, the bone is constricted to a 

 neck-like portion, but, again expanding, terminates in a rounded margin, which forms 

 the outer surface of the articular condyle for the lower jaw. For a portion of its 

 extent the anterior border of the bone overlaps the ventral termination of that portion of 

 the fronto-parietal which extends on to the outer surface of the suspensorium (fig. 1). 



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