THE CHONDROCRANIUM OF LEPIDOSTEUS. 257 



pterotic ridge of the Holostei and Teleostei, notwithstanding that 

 it does not lie along the ridge of the lateral semicircular canal. 



The hyomandibula is said by Wells to articulate with the 

 " postero-lateral surface of the cranium, in the region of the 

 horizontal semicircular canal/' and she shows it, in her figures, 

 lying much farther posteriorly than Gegenbaur shows it, and 

 than I find it in two specimens that 1 have examined. 8he 

 shows it apparently directed dorso-posteriorly, while I find it, 

 when the palato-quadrate is put in the position shown in her 

 figure 5, directed dorso-anteriorly, with its dorsal end partly 

 hidden internal to the palato-quadrate. Its articular facet lies 

 ventral to the ridge of the lateral semicircular canal, and external 

 to the ventral portion of the auditory vesicle (sacculus ?), a slight 

 ridge marking its dorsal edge. The vena jugularis lies between 

 this latter ridge and the summit of the ridge of the lateral 

 semicircular canal, and traverses a short canal through the 

 postorbital process. The" posterior opening of this canal lies 

 immediately ventral to the anterior end of the ridge of the lateral 

 semicircular canal, and is apparently not shown in Wells's figures. 

 The ridge of the lateral semicircular canal thus foi'ms the dorsal 

 edge of the groove tliat lodges the vena jugularis, and in this 

 corresponds, as will be seen latei", to tlie opisthotic ridge of 

 Polypterus. The levator maxillse superioris has its insertion, in 

 my specimen, on that part of the palato-quadrate that lies pos- 

 terior to the so-called palatine process of Wells's figure, instead 

 of anterior to that process, as shown by her, and no part of the 

 adductor mandibulre has its insertion near the anterior end of 

 the palato-quadrate. 



In Ileptcmchus, the conditions, as shown in Gegenbaur's ('72) 

 figures, are similar to those in Acanthias, but tlie anterior portion 

 of the spheno-pterotic ridge has undergone special development 

 to form an articular facet for the dorsal edge of the palato- 

 quadrate. 



In a prepared skull of a 10cm. embryo of Mustelus, I find the 

 dorso-Iateral edge of the chondrocranium formed by the ridge of 

 the lateral semicircular canal, and between this lidge and the 

 ridges of the anterior and posterior semicircular canals there is 

 a, marked supraotic depression. The postoi'bital process is but 

 slightly developed, and is hardly recognizable. In adult specimens 

 of this fish the postorbital process is strongly developed, as shown 

 in Gegenbaur's ('72) figures of this fish and of the closely related 

 Galeus, and a spheno-pterotic ridge runs postero-mesially from 

 the outer end of this process to the summit of the ridge of the 

 lateral semicii'cular canal, and there vanishes ; the spheno-pterotic 

 ridge of this fish thus forming the dorso-lateral edge of the larger 

 a,nterior portion of the otic portion of the chondrocranium, but 

 the posterior portion of that edge being formed by the ridge of 

 the lateral semicircular canal. The hyomandibula articulates 

 with the lateral surface of that part of the otic capsule that 

 lodges the ventral portion of the auditory vesicle, and there is a 



