DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 901 



and immediately behind the trabecule assume more of their earlier appearance, but with a 

 median septum projecting superiorly. In T. gurnardus, -£% inch in length, they send out 

 a lateral expansion — a pre-orbital horizontal plate, but further forward they continue in 

 the usual cylindrical form. Between the rod-like portion, which forms the main part of 

 each trabecular element, and the lateral plate, a region devoid of cartilage-cells passes, the 

 significance of which is not easily understood. As the ridge-like shape of the septum is by 

 and by more marked in Anarrhichas, and as the cartilage diminishes, the median septum 

 becomes a fibroid streak. The chief difference in the shape of the ridge-like bar of the 

 trabeculse is the slightly more bulbous condition of the outer edge in transverse section. 



Before the infundibulum is reached, the trabeculse become flat, and then separate, 

 the bars in this case sloping from below upward and outward, and between them lies a 

 firm plate of hyaline hard tissue, thickest in the middle and bevelled off as it approaches 

 the trabeculse. In front of the infundibulum a number of muscular bands pass toward 

 the eyes in the middle line, and two blood-vessels soon after rest on the floor. At the 

 infundibulum the hyaline floor diminishes, and the blood-vessels become more lateral in 

 position. Behind the infundibulum the trabecules widen out and join the basilar plate 

 forming the floor of the cranium, where the notochord commences. Thus they do not 

 again unite. A further complication occurs about the beginning of May, when two 

 slightly converging vertical bars of hyaline ossific tissue appear at the anterior ends of 

 the trabecules — passing upward from the bases of the teeth, one dental sac being, indeed, 

 placed between the limbs of the processes. The cartilage at this time is divided into an 

 upper and a lower region, the latter again being vertically subdivided. The whole nasal 

 region is cartilaginous, and further ossifications at the bases of the teeth are present. A 

 plate of the same hyaline tissue appears in the free flap at the side of the mouth, and 

 seems to represent the maxillary. 



About the end of March a nasal cartilage develops behind the olfactory sacs, being, in 

 fact, a superior process (fronto-nasal) of the trabeculse at their anterior ends. A second bar 

 of cartilage, the anterior end of the pterygo-quadrate, projects outward in horizontal sections, 

 towards the outer angle of the truncated muzzle on each side — at a somewhat lower level. 



The fronto-nasal plate in the post-larval Gadoid, ^ inch in length, is very broad and 

 massive, as indeed it is when the fish measures T 5 ^ inch in length, but there now lie on 

 each side externally two slender pre-frontal bars. The frontal rudiment appears in the 

 young Clupeoid as a plate of cartilage passing transversely over the pineal region, and the 

 fronto-nasal process below is flattened and less massive than in the Gadoids. In the 

 herring, the frontal rods, passing superiorly between the eyes, broaden out before ter- 

 minating over the cerebral lobes. Parietal rudiments appear in the gurnard, T 5 ^ inch 

 long, and a sharply pointed hyaline spine, firmly fixed to a horizontal base of the same 

 dense tissue, occurs over these paired elements. When T 9 2 inch long the pre-frontal 

 cartilages appear over the eye, outside the sclerotic cup, while below each eye are the 

 infraorbital elements. The latter are well developed in the Gadoid T 5 ^ inch in length. 

 In Callionymus, ^ inch long, the suborbital series arise as hyaline scales. In the 



