SKELETON OF EEQALECUS AEGENTEUS. 3 3 



The parietals (pa) are long narrow bones situated one on either side of the supra- 

 occipital, and elevated considerably above the level of that bone, so as to form paired 

 longitudinal crests of considerable size. Each articulates by its inner edge with the 

 supraoccipital, by its outer edge with the frontal and pterotic. The parietals do not 

 appear on the inner surface of the skull-wall. 



The frontals (fr) are the largest bones in the brain- case, forming a considerable 

 portion of its dorsal wall as well as the chief part of the supraorbital plates. They 

 differ from the homologous bones in most Teleosts in not uniting with one another, 

 either by suture or ankylosis, in the middle line ; on the contrary they are separated 

 by a wide cartilaginous interval in front, and behind by the whole width of the supra- 

 occipital and parietals. Each frontal is arched from before backwards, and produced 

 in front into an irregular plaited process (figs. 7, 11, and 12, fr), which rises well above 

 the tegmen cranii and helps to give the skull its peculiar form. It also forms the 

 greater part of the supraorbital ridge, and is produced inwards into a supraorbital 

 process (fr l ), which, together with the orbitosphenoid and alisphenoid, constitutes the 

 roof of the orbit. The frontal articulates in front with the ectethmoid, and behind 

 with the sphenotic and pterotic, overlapping the former and being overlapped by the 

 latter (cf. fig. 13); the supraorbital process articulates not only with the orbito- and 

 alisphenoid, but also to a slight extent with the prootic (fig. 12). A small part of 

 the supraorbital ridge is subcutaneous (see fig. 1). 



The parasphenoid (pa.s), as stated above, is carried far below the proper level of 

 the basis cranii, owing to the great size of the orbit. It is a gently curved bone, 

 keeled in the middle ventral line, and greatly compressed from side to side posteriorly, 

 where it forms the ventral portion of the subcranial crest. In this part of its extent 

 it is embraced above by the supraoccipital, that bone being divided below into two 

 laminae between which the parasphenoid is inserted (cf. figs. 7 and 11). In front of 

 the foramen B the parasphenoid articulates on each side with the descending plate of 

 the opisthotic (o]).o 4 ), and sends off a process which passes upwards and slightly out- 

 wards, articulating with the descending process of the sphenotic, and forming with it 

 the postorbital pillar. In front the parasphenoid underlies the prenasal cartilage, 

 and is underlain by the vomer (vo). 



The vomer (vo) is a thin slender bone, clamping the ventral edge of the prenasal 

 cartilage, and extending backwards beneath the parasphenoid. Near its anterior end 

 it sends off on each side a somewhat irregular laminar process, which is directed 

 upwards and backwards on the side of the prenasal cartilage (fig. 7). 



The following loosely attached bones are best considered in connection with the 

 brain-case. 



The nasals (fig. 6, na) are small irregularly oblong bones, attached by fibrous tissue 

 to the frontals and arching over the nostrils. 



The preorbitals (figs. 6 1 , pr.or) are two bones on each side, articulating with the 



