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



cartilaginous plate which, on each side, helps to roof in the branchial apparatus, while 

 a narrow strip of cartilage extending forward from the distal end of the suspensorium 

 along the dorsal border of the palato-pterygoid bone as far as the ethmoidal region, 

 and continuous dorsally with the lateral margin of the cartilaginous basis cranii, may 

 be regarded as representing a palato-pterygoid cartilage. Further, it may be affirmed 

 that the condyle for the lower jaw is somewhat more anteriorly situated than in 

 Lepidosiren, or, in other words, the suspensorium of Ceratodus is inclined forward to a 

 greater extent and makes a more acute angle with the fore part of the basicranial axis. 

 The identification of upper labial cartilages in Ceratodus is by no means easy to 

 determine satisfactorily. Giinther {I. c.) apparently overlooked the existence of 

 possible representatives of these structures, but subsequently two pairs of cartilages 

 were discovered by Huxley {I. c), the position and relations of which he thus 

 describes : — " One of them lies in the roof of the mouth, just in front, and on the inner 

 side, of the posterior nasal aperture. It is fixed to the mesethmoid cartilage (m.c.) by 

 fibrous bands, and is broader behind than in front. The inner edge of this cartilage is 

 concave, the outer convex, and it has a nearly horizontal direction. The second 

 cartilage [I. c. figs. 4, 5, 7, 2] is stouter, and lies behind, and on the outer side of, the 

 posterior nasal aperture. Its dorsal end is attached to the base of the skull and the 

 anterior part of the palato-pterygoid cartilage, just above the middle of the palatine 

 tooth. It then descends into the upper lip, near the angle of the mouth " (I. e. pp. 32- 

 33). Huxley's description of the first of these cartilages, which provisionally may be 

 called an anterior upper labial, is quite accurate, except that its mesial attachment is 

 rather to the internasal septum than to the mesethmoid cartilage ; and it may also be 

 added that the outer extremity of the cartilage extends into the horizontal fibrous 

 septum between the two narial apertures. On the other hand, his description of the 

 " posterior upper labial " is not quite correct, inasmuch as the dorsal attachment of 

 the cartilage is neither to the base of the skull nor to the anterior part of the palato- 

 quadrate cartilage ; on the contrary, the dorsal or proximal extremity of the cartilage 

 is connected by ligament with the fibrous suture between the ascending process of the 

 palato-pterygoid bone and the preorbital portion of the ectethmoid, and hence by the 

 sutural union of these bones the cartilage is widely separated from the chondrocranial 

 portion of the skull. It is, in fact, somewhat difficult to be quite sure that Huxley's 

 posterior labials are not the equivalents of antorbital cartilages, such as are present in 

 Lepidosiren and Protojrterus, but otherwise wholly absent in Ceratodus, and, indeed, 

 have been so considered by Rose [36], whose view is corroborated by the fact that each 

 cartilage extends downward into the upper lip, near the angle of the mouth. At the 

 same time, it is evident that these cartilages differ from the antorbital processes of 

 other Dipnoi in not being continuous posteriorly with the trabecular region of the 

 chondrocranium, although it is at least possible that this want of continuity may be 



