DEVELOPMENT OF THE SKULL IN THE SALMON. 
I O O 
OO 
until we come to the elegant quadrate condyle (q.), the angle of the “ palato-quadrate 
arch.” The hinder outline of the pier is so convex that the whole arch still retains the 
primordial curve, broken in upon by the oblique fissure which formed the joint-cavity. 
The “ articulo-Meckelian rod” (mandible, ar.,mk.) is thick and produced into an angle 
behind the selliform hollow for the quadrate ; it then continues thick and terete to its 
rounded end. The whole of the first postoral pier is let down so as to be below the 
expanded head of its successor (fig. 1), which now carries it. Thus simple is the morpho- 
logical process by which the curious protrusible mouth of a fish is constructed ! 
The bony plates and the exact form, in section, of the mouth-margining cartilages 
are shown in the sectional views. 
In the foremost of these (Plate III. fig. 7, pa.) the thick articular portion is shown 
to have at its infero-external face a delicate ectosteal lamina, the rudiment of the bony 
palatine. In the next (Plate III. fig. 8, pa.) the rod is flatter, and this is behind the 
bony plate. In the third (Plate III. fig. 9, pa., ms.pcj.) we have a perfect section of 
the mouth, and the palatine bar, much flattened, has a second bony lamina on its inner 
side, the “ mesopterygoid.” 
The former, the palatine bony plate, has precisely the same relation in the young and 
old Sturgeon, and in old specimens the mesopterygoid is also well seen*. In the same 
section is seen the maxillary (mx. ) and the Meckelian rod (ink.), perfectly round ; on one 
side both the dentary and articulare ( ar .) are seen, on the other only the dentary. 
In the fourth section (Plate IV. fig. 7), which may be profitably compared to two 
similar views of the Tadpole’s skull (“ Frog’s Skull,” Plate vi. figs. 3 & 4), the coalesced 
“palato-quadrate” is cut through, the quadrate hinge being seen (q.) and the ascending 
pterygo-palatine bar (ppcj.). Below the quadrate is the articular region with its osselet 
(ar.), and beneath the section of the tongue and mouth-floor the crown of the inverted 
second “postoral” is cut through, showing the “basi- “hypo- and “ cerato-hyals,” in 
section and in relation. The great distance of the metapterygoid apex of the first 
“ postoral” from the upturned postfrontal angle of the ear-sac is shown in the sixth 
section (Plate III. fig. 10, mt.pg) ; this part is bent outwards, the pier being in-bent where 
the two regions join: this is a correlate of the assumption of a new swinging-point, for 
the metapterygoid bends outwards to overlap the hyo-mandibular. Below the quadrate 
(q.) is the angular process of the articulare (ar.) ; below the back of the tongue (t.) is 
seen the fore end of the first basibranchial (b.br.), and on each side we see the “ cerato- 
hyals” (c.h.) obliquely cut through. 
Each hyoid ramus is now composed of four cartilages (Plate IV. fig. 1), which are 
ossified somewhat later than the arches in front ; I did not find any traces of osseous 
deposit, even in transverse sections, highly magnified : the cartilages will now be described, 
and their osseous centres when I come to the seventh stage. To understand the state 
of things, reference must be made to the first splitting up of the “ second postoral,” and 
to the changes seen in the third and fourth stages ; these have been just described. 
* See my paper iu Micr. Journ., June 1873, plate 20. fig. 5, pa., ms.pg. 
