Bkooks — The Osteology and Arthrology of the Haddock. 173 



of the bone the two prefrontals unite above the 'cartilage. In front 

 it joins both vomer and mesethmoid. 



The hyomandibular (Pl.YI., fig, 7) presents a head above, a body, 

 and three processes. The head is convex above, compressed from 

 side to side, articulating with a hollow formed by the sphenotic, pte- 

 rotic, and prootic bones. Below the head is a sliglitly constricted 

 neck, and below this externally the body spreads' out into a nearly 

 smooth triangular surface, into which is inserted a muscle (PI. YI. 

 fig. 4, /), which abducts the whole apparatus (suspensorum and 

 operculum included). The anterior border of the bone is perforated 

 in two places for the anterior and posterior branches of the facial 

 nerve. The anterior process spreads out in a fan-like form and 

 joins the metapterygoid in front, and just touches the symplectic. 

 Behind it is connected to the symplectic by a triangular piece of 

 cartilage, which articulates with the stylo-hyal.- The middle pro- 

 cess articulates firmly with the preoperculum, passing external to it. 

 Between these two processes runs a ridge, under which the tem- 

 poral muscle dips to take additional origin. The posterior process 

 stretching backwards, furnishes an articular condyle to the oper- 

 culum proper. 



The s}'mplectic is of an elongated, triangular form, with the 

 base above. The latter is connected to the hyomandibular by the 

 triangular intercalary cartilage, and (very slightly) in front of this 

 by bone. The narrow apex fits into a groove in the inner surface 

 of the quadrate. The anterior border fits into a longitudinal 

 groove on the posterior border of the metapterygoid, and the pos- 

 terior border bounds anteriorly a large fenestra (PI. YL, fio-. 5 d) 

 through which the anterior branch of the facial nerve passes. 



The quadrate furnishes an articular condyle to the mandible 

 below, which is concave from side to side, and convex from before 

 backwards. From this runs a strong ridge backwards and up- 

 wards, the postero-inferior edge of which is firmly united to the 

 preoperculum, which slightly overlaps it. On the inner surface is 

 the groove for the symplectic. Anteriorly a comparatively thin 

 scale of bone springs from the ridge, and is grooved in front for 

 the ectopterygoid, and above for the metapterygoid. 



The metapterygoid is a splint of bone, resembling the sym- 

 plectic, but smaller, more slender, with the base downwards, and 

 Jightl}^ curved, with the concavity outwards; The posterior border 



