IN THE PARAGUAYAN LEPIDOSIREN, ETC. 331 



The origin of the temporal fasciae and their relations to the bones, muscles, and 

 other structures of the head in Lepidosiren may be briefly described. The superficial 

 stratum of each of the great dorso-lateral trunk-muscles passes into a thin fibrous 

 fascia -which, after extending over the temporo-masseter muscles, blends anteriorly 

 with a fibrous ring encircling the orbit, and is also attached to the posterior curvature 

 of the antorbital cartilage, finally becoming continuous in front with the fibrous 

 investment of the nasal capsules. Inferiorly, the fascia is continuous with the touo-h 

 fibrous tissue investing the outer surface of the hinder portion of the mandible. 

 Dorsally, the fascia becomes continuous with the external margin of the supraorbital 

 bone of its side, and, reappearing on the inner margin, becomes, in turn, continuous 

 with the inner margin of the corresponding bone of the opposite side of the 

 skull 



From the relations of the two supraorbital bones to the temporal fasciae it would 

 seem at first sight that the suggestion of Wiedersheim in the case of Protopterus is 

 equally applicable to Lepidosiren. When, however, the position and relations of the 

 equivalent bones in Ceratodus are carefully examined, it is not quite so clear that the 

 name " Sehnenbein " is ivholly accurate in either instance. 



For the hinder part of its extent each supraorbital bone in the latter Dipnoid is a 

 thin but relatively much wider plate than in either Protopterus or Lepidosiren, and 

 becomes almost fibrous at its irregular free posterior margin, where it is continuous with 

 the equivalent of the more posterior portion of the temporal fascia. In this region the 

 bone lies externally to the jaw-muscles, but, unlike its representative in other Dipnoi, 

 is connected with its fellow through the intervention of a similarly-situated bony lamina 

 which is the " postero-median " bone of Huxley [15, fig. 7 b], and the " sclero parietal " 

 of Giinther [11, pi. xxxiv. fig. 4, a]. More anteriorly, as it passes over the orbit, the 

 bone thickens considerably, but nevertheless so far retains the position and relations of 

 the supraorbital bone of Lepidosiren and Protojiterus. Instead, however, of terminating 

 in the orbital region, the bone extends forward, closely investing the dorsal wall of the 

 hinder part of the cartilaginous nasal capsule, and at the same time suturally articulates 

 internally with the outer margin of the dermal ethmoid (PI. XXIX. fig. 20 ec.e.). 

 The preorbital portion of the bone forms moreover a characteristic descending 

 process which, passing downward between the orbit and the nasal capsule, becomes 

 greatly thickened laterally \ and also closely applied to the lateral wall of the chondro- 

 cranium in the region of the mesethmoid. Finally, the process terminates inferiorly 

 in a sutural articulation with the dorsal edge of an ascending lamina derived from the 

 dentigerous palatine portion of the palato-pterygoid bone (fig. 20, p.pt.a.). It is 

 obvious, therefore, that the preorbital section of the bone forms not only a partial 

 roof, but in addition a posterior wall to the olfactory capsule, and at the same time 



1 The centre of this part of the hone contains a cavity filled with fatty connective tissue. 



