506 MR. W. K. PARKER ON THE STRUCTURE AND 
gives us the first intimation of the frontal (/.) outside the orbito-sphenoid (0.s.). The 
end of the middle turbinal is seen from behind in the sphenoidal sinus (sp.s.); at 
this part the nidus of the vomer is most solid, and comes nearest to hyaline cartilage 
(fig. 14", v.), a state of things first pointed out to me by my friend Mr. Cas. Srewarr. 
The proper territories of each investing bone in the Pig evidently only want time 
that they might all become true cartilage ; ossification sets in too soon for the formation 
of the intercellular substance, but each tract, before ossification, is a true morphological 
clement or organ, as much so as the cartilaginous ** operculars” and “ branchiostegals” 
of a Shark.or the “labial cartilages” of a Myxinoid. In illustration of these remarks 
I have now to mention a fact new both to Professor HuxLey and myself, namely, that 
the substance which ossifies to become the dentary (figs. 14 & 14%, d.) becomes for the 
most part very typical solid colourless cartilage, as much so as MuckEL’s cartilage, which 
it invests: I shall show this more fully in the next stage. 
The fifteenth section (Plate XXXII. fig. 1) is through the fore edge of the optic 
foramen; and here we see the nasal wall (2.w.) closing in upon the presphenoid (p.s.), 
and joining the end of the sphenoidal sinuses. Part of each optic nerve (2) is seen in 
this section, and for that reason the orbito-sphenoid appears distant from the median 
cartilage below; its continuity is seen in the vertical section (Plate XX XIII. fig. 4). 
Here the frontal (f.) is growing down towards the orbit, to which it will form a ceiling. 
The siateenth section (Plate XXXII. fig. 2) is through the largest part of the hemi- 
spheres and the underlying thalamencephalon ; the eye is cut through near its posterior 
canthus, and the optic chiasma is severed (2). This section is through the lowest part 
of the presphenoid, which is still invested below by the vomer (v.); and opposite the 
section of the hindermost part of the ascending palatine plate we see the fore part of 
the cartilaginous “external pterygoid plates” (e.pq). The orbito-sphenoids (0.s.) are 
here at their greatest size, creeping far up the cranial wall and protecting the swelling 
hemispheres; the section through the dentary (d.) is close in front of the ‘ coronoid 
process.” 
The seventeenth section (Plate XXXII. fig. 5) is through the large orbito-sphe- 
noidal leaves, where they join the presphenoid behind the optic foramen (sce also 
Plate XXXIII. fig. 4, 0.8., ps., 2). This is the last section which shows the vomer (v.), 
and here the razor passed through the soft, faintly ossified ‘internal pterygoid plate ”— 
pterygoid proper. The fore-turned external pterygoid plates (¢.pg.) are here thick 
massive cartilages; and here, also, both the primary (mé.) and secondary (a7.) elements 
of the mandible are composed entirely of hyaline cartilage; this part of the permanent 
lower jaw is the coronoid and fore part of the articular regions. This section through 
the posterior part of the palato-pterygoid bar is of great interest, as it gives the direction 
taken by the apex of the second facial bar, namely upwards and outwards, although 
the wpward bend is less in the Pig than in many Mammals; it has its fullest develop- 
ment in that small Ruminant, Tragulus javanicus. 
In the eighteenth section the basisphenoid and its ale (Plate XXXII. fig. 4, .s., 
