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3. SUSPENSORIAL APPARATUS AND MANDIBLE. 



The PREOPERCULAR is a stout bone with dorsal and ventral limbs lying at somewhat more 

 than a right angle to each other. In their natural positions the dorsal limb is directed dorso-anteriorly 

 and the ventral limb ventro-anteriorly. The dorsal portion of the dorsal limb rests against and is 

 firmly bound by tissue to the grooved hind edge of the hyomandibular, its dorsal end not extending 

 beyond the opercular process of that bone. The ventral portion of the ventral limb rests against 

 and is firmly bound to the grooved postero-ventral surface of the posterior process of the quadrate. 

 Between these two portions of the preopercular a large and thin web of bone extends across the angle 

 between the two limbs and supports, on its internal surface near its ventral end, that part of the 

 hyomandibulo-symplectic interspace of cartilage on which lies the articular facet for the interhyal. 

 Dorsal to that facet, the web of bone is thickened to form a process-like portion, and the edge of this 

 portion is bound by tissue to the hind edge of the ventral portion of the hyomandibular. At the dorsal 

 end of the web there is an incisure, through which, between the preopercular and the hind edge of the 

 hyomandibular, the ramus hyoideus facialis passes from the outer to the inner surface of the apparatus. 



The large and well known preopercular spine of the fish extends posteriorly in the direction of 

 the ventral limb of the bone, and almost as a posterior continuation of that limb. A second one of 

 the three preopercular spines lies directly ventral to this large one, either parallel with it, or directed 

 ventro-posteriorly at an angle to it. The third preopercular spine arises from the ventral edge of the 

 ventral limb of the bone, close to its anterior end. The bone is traversed its füll length by the pre- 

 opercular latero-sensory canal and lodges five sense organs of that canal. 



The HYOMANDIBULAR has anterior and posterior heads for articulation with the cranium, 

 and a very stout head for articulation with the opercular. The shank of the bone is relatively broad 

 and thin, and the longitudinal ridge on its outer surface is short, but stout. The bone is traversed 

 by a facialis canal, which opens on the outer surface of the shank anterior to th« longitudinal ridge, 

 and also by a short branch canal which opens on the outer surface of the bone posterior to the ridge. 

 A large web of bone fills the angle between the^ anterior articular head and the shank of the bone, 

 and is in contact with and is firmly bound by tissue to the hind edge of the metapterygoid. 



The SYMPLECTIC has a broad flat dorsal end, and from there tapers rapidly into a long 

 rod-like ventral portion which lies in the symplectic groove on the inner surface of the quadrate. 

 There is a canal along its anterior edge, between it and the anterior edge of the symplectic groove 

 on the quadrate, which transmits the ramus mandibularis internus facialis. 



The QUADRATE has a stout and long posterior process which is separated from the body 

 of the bone by a shallow incisure. Anterior to the dorsal portion of the process, between it and the 

 symplectic, there is a long oval opening which transmits the ramus mandibularis externus facialis 

 and the arteria hyoidea. The posterior process of the quadrate is so long that it almost completely 

 shuts the preopercular off from bounding participation in this opening. Along the anterior edge of 

 the base of the process there is, on the inner surface of the body of the quadrate, a symplectic groove. 

 From the inner surface of the anterior edge of the bone a stout ligament arises and running forward 

 joins the tendon AaAg-Aj^. 



The METAPTERYGOID is large and flat, and without evident flanges on its hind edge. This 

 edge of the bone is however in contact with the anterior edge of the flange on the anterior edge of 



