THE OSTEOLOGY OF AMIURUS CATUS. 273 



zontal portion of the supraoccipital, are parts of the same cavity. 

 In a skull from which all accessory parts have been removed, it 

 opens by a comparatively wide opening at the base of the ridge, 

 which extends upwards upon the bone to unite with the similar 

 ridge on the supraoccipital spine. This opening is almost closed in 

 the natural condition by the supraclavicle, a small opening only 

 being left. The cavity is apparently quite shut off from any com- 

 munication with the brain-cavity, and contains only fatty tissue. 

 On the upper surface of the pterotic, on the projecting posterior 

 portion, are several foramina — the openings of a mucous canal, 

 which passes forwards in an osseous canal, running along the outer 

 edge of the bone. The smooth surface formed by pterotic, exoc- 

 cipitals and epiotic lodges the utriculus. The pterotic articulates with 

 the supraoccipital above ; the epiotics, and supraclavicular behind ; 

 the exoccipitals, and prootics below ; and in front with the sphenotic. 



6. Prootics, (PL II. Fig. 2, PrO.) 



Lie on each side immediately in front of the exoccipitals. Each 

 is a somewhat quadrate bone, extending to the middle line 

 below, where it articulates with the fellow of the opposite side, 

 thus entering into the formation of the base as well as the walls 

 of the skull. The middle portion of its inner surface is crossed 

 by a ridge, notched outwardly, in which notch the anterior or 

 sagittal semi-circular canal passes to the recessus utriculi. Near 

 the posterior edge is another smaller ridge, round the outer 

 extremity of which the same canal turns in passing forwards from 

 the utriculus. Between these two ridges is a smooth hollow, with 

 a very tliin wall, which lodges the recessus utriculi. Below the 

 prootics, where they meet in the middle line below and between them 

 and the anterior portion of the basioccipital above, and the parasphe- 

 noid below, is a small cavity. This is the almost aborted rudiment 

 of the canal for the orbital muscles, which is largely developed in 

 many fishes, but absent or very rudimentary in Silurus, Amiurus, 

 Gadus, Lophius, <fec. The middle of the anterior edge of the prootic 

 is notched variously in different individuals, sometimes possessing a 

 hingle notch, at other times there being two more or less separated 

 by an intervening osseous spicule. These notches are closed in front 

 by the posterior edge of the alisphenoid, and through the foramina 

 thus formed the fifth and seventh cranial nerves (trigeminus and 



