158 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



by the basi-occipital and opisthotic, and internally by its 

 fellow of the opposite side. It bears a conspicuous 

 foramen with a long canal (f.vg., figs. 2, 3) for the exit of 

 the vagus nerve, and at least one other for the first spinal 

 nerve. 



Supraoccipital (S.O., figs. 1, 4).— A large asymmetri- 

 cal bone hardly appearing on the occiput, from which it is 

 excluded by the epiotics, and having only a feeble 

 occipital spine (Oc.S.), so well marked in the Cod. This 

 spine and ridge is continued forwards to the left anterior 

 corner of the bone, where it forms a furrow developed in 

 connection with the interspinous bones or axonosts of that 

 part of the dorsal fin situated over the head, as elsewhere 

 described. In front the supraoccipital is thin and 

 laminate, so that the roof of the cranial cavity is here very 

 slender, but behind the cerebral surface of the bone is 

 supported by three strong ridges of bone and cartilage. 

 The supraoccipital is bounded in front by the frontals, 

 laterally by the parietals, and behind by the epiotics. 

 The basi-, ex- and supraoccipitals together form the 

 occipital segment of the cranium. 



The Auditory Capsule of the Plaice is formed by the 

 following five bones, as in the Cod : — 



Sphenotic (Sp.O., figs. 1, 2, 3). — Does not contain 

 much cartilage. Externally on the dorsal surface a strong 

 process is sent out and supported by a ridge of bone 

 coming up from below. The sphenotic forms the external 

 and upper half of the deep cup for the ball of the 

 hyomandibular (cp. fig. 5), the prootic half of the same 

 being more or less separated from it by a strip of the 

 chondrocranium (cp. the two sides in fig. 2, Hm.F. 1 ). 

 The cerebral surface of the sphenotic has two large cavities 

 separated by a thick wall of bone and cartilage. The 

 sphenotics are not quite symmetrical — that of the ocular 



