Brooks — The Osteology and AHlirology of the Haddock. 169 



wards. Just below this ridge it is perforated for a brancli of the 

 trigeminal nerve. It overlaps all the bones of the cranium with 

 which it articulates, except the frontal. If the skull be softened 

 in boiling water, it can be easily raised without disturbing the 

 other bones. It is then seen to bridge over the hiatus^ between 

 the supraoccipital and pterotic bones, both of which it overlaps for 

 some distance. It articulates also with the epiotic, sphenotic, frontal, 

 and just touches the alisphenoid. The tip of the inner limb of the 

 post-temporal fits into a groove on the upper surface behind. 



The epiotic is a very small bone, presenting a superior and an 

 external surface, placed at right angles to each other, and a narrow 

 posterior surface ; above it articulates with the parietal, and just 

 behind this supports the inner limb of the post-temporal ; internally 

 it joins the supraoccipital ; below, the exoccipital, and externally 

 the pterotic and opisthotic. Its cerebral surface is excavated by 

 the posterior vertical semicircular canal. 



The exoccipital (PI. YI., fig. 6) presents on its posterior surface a 

 convexity from side to side, and a concavity from above downwards. 

 The convexity forms a ridge, which is bent in such a manner as to 

 present a concavity outwards, which overhangs a large foramen in 

 the upper end of the bone for the vagus nerve. Below, the ridge 

 ends in a sub-cylindrical extremity, which articulates with a pro- 

 cess of the body of the atlas. Internal to the ridge, near where it 

 joins the atlas, is a foramen for the first spinal nerve. The two 

 exoccipitals, with the basioccipital, bound the foramen magnum. 

 The inner borders articulate above with the supraoccipital ; below," 

 with each other. The sutures seen on the outside of the skull are 

 with the supraoccipital, epiotic, opisthotic, and basioccipital. The 

 outer portion of the bone stretches forwards on the inner surface 

 of the opisthotic (inside the skull), and is connected to the prootic 

 and pterotic by a strip of cartilage. The upper part of the cere- 

 bral surface of the bone is notched by the lower crus of the poste- 

 rior vertical semicircular canal; and just below the internal opening 

 of the foramen for the vagus nerve is a slender, foot-like process, 

 which, articulating with a ridge on the upper surface of the basi- 



^ TMs space is also closed partially by cartilage, which underlies the parietal. 

 2 That is, by the edges of the surface which is turned towards the commencement 

 of the spinal cord. 



