10 MONOGRAPH OF TlIE FRKSll WATER III. 



preopercular is attached to the medial crest of the epitympanic, whilst the lower 

 angle articulates on the body of the articular. 



The />/>"/ rcttltir (34), is an exact crescent, on the convexity of which is situated 

 the conical spine, directed obliquely upwards. The insertion of the spine is above 

 the middle of the crescent. The concavity of the latter is occupied by a thin ex- 

 pansion of that bone, making the direct continuation of the tympanic wall. 



The ojxi-rit/m- (35), is articulated to the posterior articulating process of the 

 epitympanic. It is irregularly triangular like the hypotympauic and formed like- 

 wise of an articulating head at its summit, and of two branches, between which is 

 a thinner expansion of that bone. 



The m&opercufar (36), is provided at its lower edge with a spine whose point is 

 directed downwards and forwards, a little more conspicuous than in the figure. 

 That bone sends off two branches, a spiny one directed upwards which unit. > 

 with the inner edge of the opercular, and another thin and membranous, running 

 all along the posterior and free edge of the same bone, and in i'act, constituting the 

 actual edge of the opercular. 



The tuft rtijM i-'-tt/fif (37), is an elongated and narrow piece, very uniform in shape, 

 pointed forwards, truncated behind, extending from the subopercular behind, to the 

 hypotympanic and articular, in front. In a fleshy specimen it is not apparent, 

 being covered by the lower branch of the preopercular. AY hen the skin is removed 

 its edge may then be seen. 



Amongst the bones of the head and face there still remain to be mentioned 

 those which have been classified under the special denomination of derma-skeleton. 



To the dermo-skeleton belongs the lateral line which is described below in 'J, 

 and figured on Plate II, Fig. 11. When the lateral line enters the head, it pa.- 

 under the suprascapular into the mastoid groove, the posterior portion of which is 

 covered by two thin and small barndoor MpramcufouZf (8' 8'). From the mastoid 

 groove a cartilaginous or bony tube composed of two pieces, runs downwards into 

 the preopercular. These two tubular pieces we call the MfMtttympanic* (7 "2, I'l'), 

 being the supra temporals of Prof. Owen. 



In advance of the mastoid groove, and above the epitympanic, there arc two 

 other small tubular and horizontal pieces, our >/'//(/'/</////'/* (73 73*), of which 

 the liu-hri/uiiil (73), is the direct continuation downwards. The latter forms the 

 posterior edge of the orbit. 



The *ii/,i-l>iln/H (73'), are two in number; the posterior one is placed obliquely 

 across the cheek, from the preopercular spine to the orbit, where it meets the lach- 

 rymal tube, which passes directly into the anterior suhorhital. forming the inferior 

 of (he orbit. In advance of the latter. and near the centre of the snout, the 

 (111) may be -ecu. small, irregular, \\ith acute an.ulcs. IJetueeii the latter 

 and the prefrontal there exists a very small, insignificant ntproofbltal (71). 



'l'h<- /ii/iiii/iiin i ii-f/i is ivpie.-eiited in Fig. 5 b . The *ti/l<>lit/nl (3S) is only half 



ossified ; it is slender and el. nrjated. resting upon the epihyal. The ///////// (7.) ), 



is I. mail, short, and suliti iaugular, -jiving point- of attachment t t\vo of tin- branchi- 



The i-i'riit<ilii/<il (10i. is the largest \> ne of the Imiidean arch, elongated, 



