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ME. W. K. PAEKEE ON THE STEUCTURE AND 



gives us the first intimation of the frontal (/.) outside the orbito-sphenoid (o.s.). The 

 end of the middle turbinal is seen from behind in the sphenoidal sinus (s^.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. Chas. Stewart. 



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 Meckel's cartilage, which 

 it invests : I shall show this more fully in the next stage. 



The ffteenth section (Plate XXXII. fig. 1) is through the fore edge of the optic 

 foramen ; and here we see the nasal wall (w.w.) closing in upon the presphenoid (|>.6\), 

 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 XXXIII. fig. 4). 

 Here the frontal (f.) is growing down towards the orbit, to which it will form a ceiling. 



The sixteenth 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.j^g). The orbito-sphenoids (0.5.} are 

 here at their greatest size, creeping far up the cranial Avail 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. 3) is through the large orbito-sphe- 

 noidal leaves, where they join the presphenoid behind the optic foramen (see also 

 Plate XXXIII. fig. 4, o.s., 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 {e.pg.) are here thick 

 massive cartilages; and here, also, both the j)rimary [mk.) and secondary [ar.) elements 

 of the mandible are composed entirely of hyaline cartilage ; this part of the permanent 

 lower jaAV is the coronoid and fore part of the articular regions. This section tlirough 

 the posterior part of the palato-ptorygoid 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 upward bend is less in the Pig than in many Mammals ; it has its fullest develop- 

 ment in that small Jluminant, Tragnlus javanicus. 



In the eighteenth section the basisphcnoid and its alw (Plate XXXII. fig. 4, h.s., 



