8 H. B. POLLARD. 



of the orbital region is complete and passes into the ethmoid region. 

 At its anterior limit there is a foramen, the Canalis praeorbitalis 

 (Pr. orb. a). At the junction of the orbital and ethmoidal regions the 

 epiphysial bar (Eph.) passes across the supracranial fontanelle, thus 

 dividing the latter into pre- and post-epiphysial portions. 



The side wall of the skull is produced into a large vertical antorbital 

 process, separating the nasal and orbital cavities, and the cranium is 

 almost as wide in this region as in the auditory region. At its antero- 

 lateral extremity, the antorbital process has an articulation for the 

 prepalatine piece (Prepal.). The nasal cavities are wide apart, the 

 rostral portion of the chondrocranium being very broad. The olfactory 

 lobes and nerves lie, as it were, in two short tunnels, being separated 

 by a thick internasal septum and roofed over by the bridge of cartilage, 

 which extends from the anterosuperior orbital region to the rostral 

 region. Between the antorbital process and the base of the rostral 

 region lies the extensive floor of the nasal cavity. The shape of the 

 rostral region is best shown by the figure (Fig. 3). 



The hyomandibular (H.M.) articulates, as above mentioned, with 

 the pterotic region of the auditory capsule. Its upper portion is in the 

 form of an inverted triangle, the articulation being the base of the tri- 

 angle. At the apex of this triangular part there is a notch in front for 

 the hyomandibular nerve, while behind is attached the opercular cartilage 

 which bears the operculum. 



From this level the hyomandibular cartilage broadens downwards 

 and forwards to the quadrate and symplectic regions. At the posterior 

 ventral angle, that is in the symplectic region, is attached the stylohyal, 

 while at the most ventral, or quadrate region, is situated the articu- 

 lation for the lower jaw. Inwardly and forwards, the quadrate is pro- 

 longed into the small pterygoid process, w T hich in Silurus is attached 

 by a ligament to the vomer. 



The prepalatine piece articulates with the antorbital process. It is 

 an irregularly shaped block of cartilage. In some specimens there may 

 be found at its anterior edge accessory nodules of cartilage. Externally 

 it bears the procartilaginous axis of the maxillary barbel (Mx. t.), 

 which proceeds out at a right angle for a short distance, then turning 

 backwards. The prepalatine piece has no connection with the ptery- 

 goid process. 



In front of the rostrum is a small triangular block (Pmx. p.) repre- 

 senting somewhat schematically the premaxillary block of precartilage. 



