DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 899 



below the epithelial layer and the sensory cushions, and internal to the auditory ganglion, 

 beneath which, and over the upper surface of the parachordal cartilages, it extends as a 

 well-marked stratum. In the cod, T \ inch long, the medulla is arched over by a deeply 

 angular supraoccipital cartilage, having the form of an inverted V, and upon its sloping 

 surface on each side a flat sheet of muscle passes. A little behind, these plates in the 

 wolf-fish join a cartilaginous lamina, which bends upward and outward to form the floor 

 of the auditory chamber on each side. In the median line above the tip of the notochord, 

 and extending in front of it, is the infundibulum, but it disappears in the line of the 

 laminae forming the otocystic floors. After its disappearance the cartilaginous plates 

 (parachordals) greatly increase in bulk, so that the notochord between them is strongly 

 buttressed. Posteriorly, however, the density of the plates diminishes, and they spread 

 outward, extending under the auditory sacs. Two thickenings occur here, one externally 

 and another internally. With the former is fused the hyomandibular element. The 

 thin band connecting the two parts mentioned gives way as one of the semicircular canals 

 (probably the horizontal) comes in the line of section, and only connective tissue there 

 unites them. They seem to be closely connected behind, though this could not be accu- 

 rately made out. A similar disconnection is noticeable in the post-larval Gadoid, |^ inch 

 in length, — the basilar plate sending up ex-occipital elements to the upper posterior face of 

 the otocysts, the cartilage of both being continuous, while below is a well-marked interval. 



The tendency of the auditory capsule in Anarrhichas to sink downward is occasioned 

 by the disappearance of the cartilaginous floor just described. The cartilaginous support 

 of the notochord in transverse section now assumes the form of a broadly lanceolate process 

 seated upon each side, the outer end abutting on the wall of the descending auditory 

 sac, while the inner envelops the notochord. The cartilage curves upward fully half- 

 way round the medulla, leaving the lower part of the notochord free. It then disappears, 

 and the notochord, which has not at this point attained its full dimensions, is surrounded 

 by perichordal connective tissue (by which also the side of the neurochord is clothed) 

 supported by the muscle-plates. 



An evident difference between the foregoing arrangement, and that in the salmon one 

 day old, is the fact that the trabeculse, while united and large anteriorly, diminish on their 

 way backward, thin off in the middle, and then separate in the ocular region, becoming 

 still less as well as more widely separated as they proceed backward. In the infundibular 

 region, they again increase in size, but are separated by a considerable interval, and, 

 shortly after the commencement of the auditory capsules, the anterior end of which is 

 cartilaginous, a plate passes from them, with a slight obliquity upward and outward, and 

 joins the cartilaginous boundary confined in this region to the floor and outer wall. The 

 curvature of this floor quite differs from that in Anarrhichas, for, like Gobius and other 

 forms, it is nearly flat. The hyomandibular, forming a buttress at this point, is narrow 

 superiorly and more dilated inferiorly (more truly clavate) than in the wolf-fish. The 

 pointed anterior end of the notochord now intervenes between the plates, which, however, 

 do not touch it. Each plate somewhat behind this region becomes stouter ; but the 



