900 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



lateral extension joining the ventral auditory plate diminishes, while the auditory capsule 

 passes upward, and forms a dense structure superiorly — below the anterior semicircular 

 canal. Then the basilar plates separate from the auditory capsules, and form, in section, 

 an elliptical rod at each side, increasing in bulk further back, and again sending out a 

 lateral plate to join the floor of the auditory capsule, and finally separating from it. 

 Thereafter, each lengthens upward and outward, and joins the continuous cartilaginous 

 mass bounding the auditory capsule posteriorly. Behind the latter capsule the cartilage 

 passes upward from the sides of the neurochord, diminishing as it goes, nearly to the 

 middle line of the dorsum. In sections further back we see it diminish to a lateral plate, 

 pointed above, broad where it clasps the notochord, then broad above and pointed below, 

 and still further back it disappears. There are material differences, therefore, in the car- 

 tilaginous elements of the two forms, one of the most marked being the larger size of the 

 ear-capsules, and the deficiency of cartilage posteriorly in Anarrhichas, and the greater 

 bulk of the cartilage at each side of the notochord behind the auditory region in the same 

 form. The cartilage is evidently much more firm than in the salmon, and instead of 

 collapsing the notochord, as before mentioned, remains circular. The cartilages of the 

 posterior part of the cranium are, however, of greater complexity in the salmon. Further, 

 in the latter form a slender bar represents the palato -pterygoid ; but in the wolf-fish no 

 trace of it is present. Its position in the salmon is very different, for, as Mr Parker 

 points out, it (his palatine) lies under the eye on each side, and each widely diverges from 

 the other, whereas in Anarrhichas these bars are much nearer the trabeculse. 



Early in February (about the 10th) the pterygo-quadrate bar appears in Anarrhichas. 

 In transverse section it has the form of a small cartilaginous rod in the anterior region of 

 the snout (PL XXIII. fig. 1), just beneath the outer edge of the trabeculse, which form a 

 ridge in section. The bar seems to increase from before backward, and on 16th March the 

 trabecular floor has gained so much in breadth, in the mid-region, that it lies on each side 

 within the margin of the said floor inferiorly. Behind this, however, the trabeculse form 

 a narrow ridge, and the pterygo-quadrate bar passes outward on each side, and assumes 

 an ovoid form in the subcutaneous tissue on the roof of the mouth. It is visible at this 

 stage as far back as the pituitary body. 



As development proceeds the anterior end of the trabeculse becomes enlarged, and 

 extends upwards in the olfactory region. This is distinctly seen on 16th March (PL 

 XXIII. fig. 3). 



On 6th April, a considerable vertical extension of the trabeculse — most conspicuous a 

 little behind the tip of the snout — has taken place. In transverse section it presents a 

 somewhat hastate outline — broad and bluntly pointed below (with a median notch) con- 

 stricted above this, and then slightly dilating upward. The united trabeculse do not yet 

 come in contact with the rounded anterior ends of the pterygo-quadrate bar, but after 

 reduction in depth and assuming the shape of a broad inverted V, they reach the brain, and 

 become continuous with a broad bar of cartilage passing upward to the dorsum on each side 

 on the inner border of the eye. Beneath the anterior brain-mass are the crucial muscles, 



