316 



ME. W. K. PAEKEE ON THE STEUCTUEE AND 



frontals (/".), the true olfactory region, and the zygomatic process of the maxillary (z.mx.) ; 

 above this is the overlapping malar or jugal (j.) The thick frontal slabs send inwards 

 and downwards an " orbital plate," which clamps the ethmoidal wall ; this wall is seen 

 to be separated by a very large space from the fore top of the septum or perpendicular 

 ethmoid {]).e.), on each side of which lie the olfactory crura (1), and above these the 

 fore part of the hemispheres (C 1"). Here we see that the comb-like floor of the 

 olfactory crura (Plate XXXIV. figs. 6, 6, cr.]).) is connected with, and is the top of, a 

 system of cartilaginous ingrowths, the upper and middle turbinals (u.tb., m.tb.), which, 

 by repeated splitting, as it were, or rather by a process of foliation, is becoming more 

 complex day by day. This section is through the most solid part of the vomer (v.), 

 Avhere it is squared below to rest upon the " hard palate " over its median suture ; here 

 the palatines are cut through their fore part, where they are thin bony scoops, protecting 

 the outside of the posterior nostril passage. Large tooth-pulps [t.j).) are seen above and 

 below, and the lower are in relation to a large dentary groove, the outer wall of which 

 is very massive and the inner a smaller rod : both of these sections are parts of a con- 

 tinuous dentary (d.) ; below the inner bony bar is the Meckelian rod (mk.), on each side 

 of the base of the tongue {tg.}. 



The seventh section (Plate XXXIII. fig. 5) is through the fore part of the eyeballs 

 (e.) and the sj^henoidal sinuses (sjJ.s.), the hinder part of the backwardly projected nasal 

 labyrinth. At this point the septum, " perpendicular ethmoid," ends; and the pyriform 

 section seen here, at the posterior end of the large " rhinencephalic fossae" (see Plate 

 XXXIV. fig. 6, ol., cr.2).), is no longer indebted to the inturned nasal roofs for its height, 

 wliich is due to the upgrowth of the trabecular crests*. This section is through the 

 most solid part of the palatines {'pa.), and their interior edge is thickening and growing 

 inwards ready to form their part of the hard palate. Only the malar (j.) is seen on 

 the side and below, and mesiad of it is the coronoid process of the lower jaw (cr.). 

 Meckel's cartilage (mk.) is now high up the inside of the jaw, which is here mainly 

 composed of solid hyaline cartilage, the inner cells of which are rapidly proliferating as 

 " osteoblasts." In the root of the tongue (tg.) the ceratohyals are seen articulating with 

 the basi- and tliyrohyals [c.hy., b.hi/., th.h.), now one piece of cartilage. 



The eighth section (Plate XXXIII. fig. 6) is one of the most instructive ; it severs the 

 orbito-sphenoids (o.s.) where they pass into the presphenoidal trabecular wall close at 

 the back of the sphenoidal sinuses (see also in third stage, Plate XXXII. fig. 1). This 

 is the high part immediately in front of the optic foramina (Plate XXXIV. figs. 1, 5, 

 6, 2). The orbito-sphenoids are ovc^rlapped above by the frontals (/.), and the presphenoid 

 has the end of the vomer (v.) beneath it. Here the thin ascending plate of the pterygoid, 

 and its thick " hamular " part, is cut through ; the osseous matter is scarcely continuous 

 in the ascending part, and every now and then a separate " mesopterygoid" is developed. 



* J f tlic reader wislics to sec an exact counterpart of this structure displayed in the second facial arch or 

 '• palato-ptcrygoid,'' it is ready at hand in tlu; skull of the Pelican, -where both the preoral arches form a long 

 and solid "commissure," from whicli a liigh crest ascends. 



