82 PROF. W. K. PAEKEE, ON THE STEUCTURE OF 



behind the co-adapted upper spurs, the base of the cartilaginous orbital septum (p.s, 

 p. e) is seen, with a widening membranous space on each side of it as the pterygoids 

 diverge backwards. These bones (fig. 2, })(!) are one half longer than the palatines, and 

 they pass obliquely inside these bones, and then send out a triangular spur close 

 behind the suture. Then they seem to lessen to one half their front width; but this 

 is due to a change in the direction of the expanded part from horizontal to vertical. 



Their hinder part is the broader by far, and is a large reniform lobe (fig. 1), which is 

 lowest opposite the ascending jugal bone (j), and then rises to be attached by ligament 

 to the quadrate {q). Instead of passing within that bone, it comes short of it by a definite 

 space. Behind the sinuous inner margin of the flat part, the pterygoid has an oblique 

 facet of cartilage, which lies obliquely over and outside a similar facet on the "basi- 

 pterygoid " (i-jyg-)- Attached to the outer spur of the pterygoid, and wedged between 

 it and the jugal process of the maxillary, is a four-cornered oblique plate of bone, one 

 third the size of the palatine ; this is the " transpalatine " (t.jm). This bone forms, with 

 the pterygoid, the hind boundary of a large oval palatine fenestra, the outer wall of 

 which is formed by the maxillary and the inner by the palatine. 



The investing bones of the lower jaw (Plate XVI. fig. 1, and Plate XVII. fig. 1) 

 are a den,se well-compacted series of splints. The dcntary (d) is much the largest of 

 these, and occupies nearly all the outer face of the jaw and carries all the teeth ; it is 

 seen, above and below, on the inner side. On the outside, within and behind the 

 dentary, the articulare (ar) is invested with the angukre (ag), a small style ; the supra- 

 angulare {s.aq), is a wider plate, which overlaps the jaw and is seen most on the inner 

 side (Plate XVII. fig. 1). On the inner side, in turn overlapping the supra-angulare, we 

 see the large four-cornered coronoid (cr), whose upper angle forms the crest or coronoid 

 part of the jaw ; it bends down upon the supra-angulare behind, the articulare below, and 

 the dentary and splenial in front. The latter bone (Plate XVII. fig. 1, s/>) is a tliin 

 lath of bone, widest in front, where it reaches the chin, and narrowest behind; it 

 hides the upper edge of Meckel's cartilage (mk). 



B. The Endocranium. 



The inner part of the skull is composed of membrane, cartilage, and bone ; the hind 

 part is largely ossified, but keeps most of the subdividing synchondroses. The fore part 

 is cartilaginous, with subcentral calcifications running in certain lines between the orbits ; 

 the ethmoidal and nasal regions are free even from this deposit (Plate XVII. figs. 1-4). 

 In front of the postcrauial roof there is a long pyriform fontanelle ; and the tract 

 between the eye and ear is largely membranous. This arises from the arrest of the 

 alisphenoid(a/.s) ; the orbitosphenoidal tracts are very narrow, and become mere lips to 

 the orbital se])tum, only spreading again in the cribriform region^ where the olfactory 



