Brooks — The Osteology and Arthrology of the Haddock. 179 



cartilage, Lut which is a peculiar condensed fibrous tissue.. The 

 posterior maxillo-mandibular lig-araent is a band of white fibrous 

 tissue, into which a small muscle^ is inserted. The anterior 

 maxillo-mandibular ligament contains a very remarkable struc- 

 ture — it is a rod-like body, attached to the dentary below, and 

 tapering to a point above ; in the lower part it consists of fibro- 

 cartilage, containing large, well-developed cartilage cells in a 

 network of white fibres ; in the upper part it passes into fibrous 

 tissue. The position of this body is ■ identical with that of the 

 lower labial cartilage in elasmobranchs, the dentary being a mem- 

 brane ossification covering Meckel's cartilage (which forms the 

 lower jaw in cartilaginous fishes), and from the fact of it contain- 

 ing cartilage it may be the homologue of that structure ; in the 

 groove between the premaxilla and its inferior process there is a 

 structure very similar in appearance, the tissue being identical 

 with that of the upjoer part of the lower ligament (containing no 

 cartilage cells). Ligamentous fibres' connect the two halves of the 

 mandible together, and the four bones of the operculum are simi- 

 larly connected ; a strong ligament passes from the interoperculum 

 to the angular, and the head of the hyomandibular is kept in place 

 by a capsular ligament. Two other structures, though (strictly 

 speaking) membranes, act somewhat the part of ligaments : these 

 are, the interorbital septum and a membrane which connects the 

 palatoquadrate arch with the skull. The latter membrane is 

 attached to the prootic and parasphenoid, and stretches across to 

 the meta-, ento-, and ecto-pterygoid and palate bones, and forms 

 the floor of the orbit. The interorbital septum consists of two sym- 

 metrical laminae of fibres, which fuse into one in the centre of the 

 structure ; ^ it is attached to the parasphenoid, prootic, alisphenoid, 

 frontal, and prefrontal bones ; it closes in the posterior (large) 

 division of the. cranium (except at the uppermost part) in front; 

 and is perforated by the optic, motor oculi, pathetic, and abducens 

 nerves, while the trigeminal and facial nerves pass out between it 

 and the prootic bone ; below this the two layers fuse, and dipping 

 into the pit for the origin of the recti muscles, are attached along 

 the middle of the upper surface of the parasphenoid : above, the two 



^ Cilvier {op cit., vol. iv., L, p. 172) mentions this as " un muscle carre." 

 ^ Or perhaps a single lamina splitting above and below. 



