194 ON THE STRUCTURE OF THE SKULL. 



olfactory capsule. The eye lies over the triangular space 

 inclosed between the sides of the skull and these two processes, 

 so that e, g, f may be termed the sub-ocular arch. 



If the skull is viewed from below, the processes e and e 

 of opposite sides are seen to be continued into one another by a 

 transverse band of cartilage, which forms the proper anterior 

 boundary of the skull. The front edge of this band, which 

 Midler calls the " hard palate," articulates with the broad and 

 expanded cartilaginous plate (a). The common roots of the 

 processes f and h are also continued into a " basi-occipital ' 

 plate of cartilage, but, between this plate and the " hard palate," 

 there is an oval space through which the neck of the long olfac- 

 tory csecuni (o, Fig. 75) passes. This caecum, therefore, separates 

 the front part of the floor of the cranial cavity, which is simply 

 membranous, from the so-called " hard palate." On com- 

 paring this skull with that of the embryonic fish (see Fig. 72), h 

 obviously answers to the stylo-hyal cartilage ; /, to the ascending 

 posterior cms of the palato-quadrate inverted arch and the hyo- 

 mandibular cartilage ; e, to the ascending and anterior crus of 

 the same. It is true that no natural division of the arch into 

 palato-quadrate and hyomandibular (and symplectic) portions 

 occurs in the lamprey, but this is only one of several respects in 

 which the Marsipobranchs resemble Amphibia rather than osseous 

 fishes. The inverted cartilaginous arch which gives attachment 

 to the hyoidean and mandibular apparatuses of a tadpole is 

 strictly comparable to the arch (e, g, f) in the lamprey. The 

 margins of the oval space upon the base of the skull answer to 

 the divergent trabecular cranii, and the plate a to the ethmo- 

 vomerine cartilage. The remarkable and apparently anoma- 

 lous separation of the basis cranii into an upper membranous 

 and a lower cartilaginous part, by the interposition of the back 

 ward prolongation of the olfactory chamber, seems to me to 

 be comparable to that separation of the upper and lower walls 

 of the pre-sphenoid, basi-sphenoid, and even of the basi-occipital, 

 by a backward extension of the olfactory cavities, which takes 

 place in so many of the Mammalia. On the other hand, I doubt 

 whether the accessory buccal cartilages, 1, 2, 3, &c, can be 

 strictly compared with anything in other fishes, though some of 



