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triangulär, with curved edges. Its ventral edge fits onto tlie outer surface of tlie second infraorbital, 

 its hind edge overlapping and resting upon tlie anterior edge of the preopercular, and extending 

 nearly to its dorsal end. Its concave anterior edge forms the posterior boundary of the orbit. Its 

 dorsal end does not quite reach the lateral edge of the postfrontal. These two bones are traversed 

 by the main infraorbital canal, and each lodges one organ of that line. 



3. SUSPENSORIAL APPARATUS AND MANDJBLE. 



The QUADRATE has the usual shape, with its ventral corner enlarged to form the articular 

 head for the mandible. Its antero-ventral edge is bevelled, and fits into the grooved hind edge of the 

 ventral Umb of the ectopterygoid. Its ventro-posterior edge is greatly thickened, is prolonged dorso- 

 posteriorly in a short sharp posterior process, and between this process and the body of the bone, 

 on the internal surface of the element, there is a large symplectic groove. The ventro-posterior surface 

 of the posterior process is grooved and fits against and is firmly bound to the anterior edge of the ven- 

 tral end of the preopercular. The lateral surface of the process is raised in a large and tall ridge, the 

 outer surface of which is roughened and gives support to, and is firmly bound to, the ventro-posterior 

 corner of the second infraorbital bone. The dorso -posterior end of this raised portion fits into a small 

 notch in the anterior edge of the preopercular. Between this raised portion of the process and the 

 external surface of the body of the quadrate, there is a large depression which seems to have no special 

 morphological significance. 



The METAPTERYGOID has its dorso-anterior edge bent slightly inward, and has lateral 

 and mesial flanges along its hind edge. The mesial flange is a small one excepting at its dorsal end 

 where it is prolonged into a process which meets, or almost meets a flat process that projects antero- 

 ventrally from the anterior edge of the thin web of bone that fills the space between the anterior 

 articular arm of the hj-omandibular and the shank of that bone, and is bound to that process by 

 fibrous tissues. Ventral to this process-like portion, the hind edge of the mesial flange is connected 

 by £. wide sheet of membrane with the shank of the hyomandibular. The lateral flange projects 

 postero-laterally at a slight angle to the body of the bone, and reaches, or overlaps slightly, and is 

 attached to the outer surface of the ventral end of the shank of the hyomandibular. The ventral 

 corner of this lateral flange approaches, or may even reach and rest upon the outer surface of the 

 cartilaginous interspace between the hyomandibular and symplectic; and there is, in the corner 

 of the flange, an incisure which, with the adjoining cartilage and th-e hyomandibular, forms a foramen 

 which transmits the arteria hyoidea. 



The ECTOPTERYGOID has the usual two limbs lying at an obtuse angle to each other, 

 the dorso-anterior limb being a large plate the dorsal edge of which is grooved. This groove lodges 

 the ventral edge of the anterior end of the entopterygoid, and also that part of the palatine bone 

 and cartilage that forms the posterior ethmoid process of the apparatus, the lateral edge of the groove 

 being a tall plate which lines the lateral surface of the palatine cartilage and may even project dorso- 

 posteriorly slightly beyond the cartilage. The anterior edge of this part of the ectopterygoid is 

 somewhat jagged, and suturates with the hind edge of the ventral flange of the palatine. The ventro- 

 posterior limb of the bone is grooved on its posterior surface and fits against the antero-ventral edge 

 of the quadrate. 



