358 PROF. T. W. BRIDGE ON THE MORPHOLOGY OF THE SKULL 



Although previously unnoticed, or at all events unrecorded \ a well-marked basi- 

 cranial vacuity or cleft is present, and may be seen in a ventral view of the skull close 

 to the hinder margin of the palatine symphysis. It is oval in shape, and filled up by a 

 thick fibrous sheet continuous internally with the fibrous mass which occupies the 

 ethmoidal portion of the cranial cavity. 



From a comparison of the figure of a plastic model of the nasal region given by Rose 

 (I. c. fig. 4) with a similar model of the same region figured by himself, Pinkus 

 (7. c. fig. 7) infers that the cartilaginous lamina? which separate the oval vacuities in 

 the nasal roof increase in number with the growth of the fish and still further 

 subdivide pre-existing vacuities. 



No mention is made of the existence of upper labial cartilages in Protopterus either 

 by Owen or Cobbold, or even in the excellent and much more recent paper by Wieders- 

 heim. According to Huxley [16] there are "two upper labial cartilages — one 

 fibro-cartilaginous immediately behind the anterior narial aperture, and the other 

 behind the posterior narial opening. These answer to the upper labial cartilages of 

 Chimwra and Cestracion" (I. c. p. 181). Rose (I. c.) describes two pairs of upper 

 labials, an anterior pair represented by the terminal lobes of the prenasal process, and 

 a posterior pair which evidently correspond to the thickened and laterally-recurved 

 anterior margins of the nasal capsules in Lepidosiren. Peters (I. c.) has also figured, 

 but without describing, two pairs of upper labials. 



Huxley's account is not very clear, but from his statement of their position I think 

 there can be no doubt that his anterior labials are really the subnasal cartilages, 

 and not true labials at all, while his description of the posterior labials leaves one in 

 doubt whether he is referring to the antorbital cartilages or to the equivalents of the 

 undoubted upper labials of Lepidosiren. The identification of upper labials given by 

 Rose is certainly based on insufficient evidence, inasmuch as there is at present no 

 reason to believe that the cartilages which he terms labials have developed indepen- 

 dently of the nasal region of the chondrocranium, and I have already given reasons for 

 the view that his posterior labials are persistent trabecular cornua, such as not 

 infrequently form the anterior walls of the nasal capsules in many Anurous Amphibia. 

 The posterior labials of Peters are really the antorbital processes, but from their 

 position it would seem probable that the structures figured by him (I. c.) as anterior 

 labials are the representatives in Protopterus of the single pair of upper labials of 

 Lepidosiren. 



With the object of clearing up the obscurity as to the existence of upper labials in 

 Protoptem^ I made a careful examination of a skull of this Diunoid, with the result 

 that there is no doubt that Protopterus and Lepidosiren are in close agreement so far 



1 A linear shading in one of Peters's figures (I. c. Taf. ii. fig. 3) may be intended to represent this vacuity, 

 but no further reference is made to it, either in the figure or in the text. 



