THE SKULL OF ACANTHIAS VULGARIS 431 



ia an oblique ridge extending from the coronoid process for- 

 wards and downwards and marking the anterior limits of the 

 insertion of the adductor rnandibularis muscle. 



Connected with the jaws are the labial cartilages, these being 

 imbedded in the muscular and other Id ~ernal to the upper 



jaw fig. 9. / : . /- . The larger pair v-nds laterally from 



near the pterygoquadrate. symphysis to a point nearly below 

 the expansion for the adductor muscle where it connects with 

 a ventral element. The second labi- re imbedded in a 



similar way on the anterior face of the Meckelian cartii i . 

 though they are far ^nsive. 



Between the mandibular and the second hyoid; arch is the 

 spiracle, the anterior wall of which is supported by two small 

 flat cartilage bars : _ v which are connected by a broad L_ - 

 ment. which in turn, is attached to the cranium under the levator 

 maxillae superior muscle rigs. 3 and 5) on the dorsal 



portion of the postorbital proc-' - 



The second or hyoid arch cor.- a pair of cartilage rods 



attached at their dorsal ends to the cranium and united ven- 

 trally by a broad unpaired plate of cartilage, the basihyal 

 Each half of the hyoid arch is divided into two bars, compara- 

 ble, in a way. to the pterygoquadrate and Meckel's cartilage 

 of the mandibular arch. These halves are. a dorsal hyoman- 

 dibular which articulates with the cranium, and a ven- 



tral ceratohya. The hyomandibular is relatively short 



and stout, and acts - the suspensor of the jaws. Its upper end 

 has a slight knob-like thickening and it curves somewhat me- 

 dially, to articulate with he postero-lateral surface of the 

 cranium in the region of the horizontal semicircular canal. 

 The lower end. antero-dorsal to its connection with 

 hyal. has a flat thickened area for the attachment of a ligament 

 connecting the hyomandibular cartilage with the lower jaw. 

 The hyomandibular bears gill ray- on its postero ventral 



margin and has depressed surfaces for muscle attaching 

 Its distal end connects with the ceratohyal. a long slender bar 



Iso bearing gill rays on its postero- ventral margin . which 

 articulates with the median bas^Lya"- The latter > 



