THE SKULLS OF FISHES. 199 



monk fish (Figs. 79 and 80). The form of the skull is here the 

 exact converse of that observed in the Chimaoroids, being exceed- 

 ingly broad and depressed, instead of high and compressed. 

 The surface of the cranium is encrusted with a pavement of 

 minute ossicles, arising from the ossification of the superficial 

 layer of the cartilage. Behind, the basilar region of the skull 

 presents two lateral articular surfaces to the front part of the 

 spinal column, and exhibits the wide lateral expansions for the 

 auditory organs (An) ; at the sides of the skull, in front of these, 

 lie the orbits (Or) bounded behind by the post-orbital processes 

 (c), and by the antorbital, or prefrontal, processes (b) anteriorly. 

 The latter divide the orbits from the nasal chambers (N), the 

 apertures of which look downwards. The prefrontal processes 

 are continued, on the inner sides of the nasal chambers, into a 

 broad plate, emarginate anteriorly, which terminates the floor of 

 the skull, and corresponds with the ethmo-vomerine part of the 

 cartilaginous skull of the human foetus or of the pike. The 

 anterior part of the roof of the skull is not directly continued 

 into the upper surface of the plate, but ends in a deeply concave 

 edge ; the vacuity, or fontanelle, is occupied by fibrous tissue in 

 the recent state. Small apertures upon the roof of the occipital 

 region communicate with the auditory chambers. The upper 

 end of a stout prismatic cartilage (g) is moveably articulated with 

 the outer w r all of the auditory prominence. The lower end of 

 this cartilage is united by ligaments behind to the hyoidean arch 

 (Sy), and in front to the upper and lower dentigerous arches 

 (h and Mri). Each of these arches is composed of two pieces 

 united in a median symphysis, and the under surf^cCo of the 

 outer and posterior ends of the upper arch are articulated with 

 the upper surfaces of the outer and posterior ends of the low r er 

 arch. The upper arch is, in addition, articulated with the under 

 surface of the prefrontal region of the skull. Three cartilages 

 (i, h, I), connected together by ligaments, lie outside the denti- 

 gerous arches, two, on each side, being superior and one inferior. 

 Furthermore, cartilaginous filaments (Op) are attached to the 

 hinder edge of the prismatic cartilage (d), and to the hyoidean 

 arch (Br). 



The interpretation of the cartilages (i, k, 1) has been a matter 



