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Show b rT' 79) nd from the siJe Ji igs. 79 and 80.-The skull of Squatina viewed from a ove : '.Ig. . ' a ost-auditory pro- ( Fig. 80).-a, vomerine region; b, -rr?frontal; c, post-orbital' ~· p . h u er drncesses. e occipital condyles; f, occipital foramen; g, suspensodi!tum' h'aulpbper. Or, ' ' . 0 , 01 71(: doble . Au au l ory c < ' tigerous arch ; i, ll, l, labiat cart! ages ; 1 ' n, ~an. 1 ' 0 ' • Br branchiostegal orbit; N, nasnl chamber ; Op, opercular cart1lagmous filaments, ' rays; Hy, hyoidean arch. THE SKULLS Oli' l!'I Sll}!jS. 199 n1onk fish (Figs. 79 and 80). Tho form of the skull is here the exact converse of that observed in tho Chimmroids, being exceedingly 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 cartilag0. 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 (Au) ; 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 antorhital, 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 fmtus 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 moveaLly articulated with the outer wall of the auditory prominence. The lower end of this cartilage is united by ligaments behind to the hyoidean arch (Hy), and in front to the upper and lower dentigerous arches (h and Mn ). Each of these arches is composed of two pieces united in a median symphysis, and the under surfaces of the outer and posterior ends of the upper arch are articulated with the upper surfaces of the outer and posterior ends of the lower arch. The upper arch is, in addition, articulated with the under surface of the prefrontal region of t.he skull. Three cartilages (i, k, l), connected together by ligaments, lie outside the dentigerous 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, Jr., l) has been a matter |
