THE DOGFISH 347 



cranium. (1) On the roof lies the anterior fontanelle which 

 we have already mentioned. (2) At the front end two 

 large foramina put the cranial cavity in continuity with those 

 of the nasal capsules. Through these the olfactory nerves 

 pass from the surface of each olfactory lobe of the brain 

 into the olfactory organ. (3) On each side wall numerous 

 openings allow the passage of nerves and blood vessels to 

 and from the orbit. The relative sizes and positions of 

 these are seen in Fig. 248. (4) Just behind the auditory 

 capsules, at the bottom of a deep pit, is the foramen for the 

 ninth nerve, and on each side of the occipital condyles is a 

 foramen for the passage of the tenth nerve. (5) On the 

 under side there may be seen two shallow grooves, along 

 which the internal carotid arteries run. Where these meet 

 there is a small opening, through which the two arteries 

 enter the cranium. At the outer ends of the grooves are 

 the openings through which the external carotid arteries 

 pass from the roof of the mouth to the orbits. (6) At the 

 hinder end of the skull is the large foramen magnum. The 

 visceral skeleton is a series of seven arches, each consisting 

 of several pieces, which lie at the sides of the mouth. The 

 first of these is the mandibular arch, which forms the 

 skeleton of the jaws. Each half of the upper jaw-bar or 

 palato-pterygo-quadrate cartilage is a rod which meets its 

 fellow in front of the mouth and is there joined to it by a 

 ligament. It is attached to the cranium in front of the 

 orbit by the ethmopalatine ligament and behind to the 

 auditory capsule by a postspiracular ligament. Each half 

 of the lower jaw is formed by Meckel's cartilage, which is 

 a wide, flat bar, tapering forwards to a point, where it is 

 joined with its fellow by a ligament. It articulates behind 

 with the palato-pterygo-quadrate cartilage and is joined 

 by ligament to the hyomandibular cartilage which forms its 

 principal attachment to the skull. The second or hyoid arch 

 consists of two pieces, an upper hyomandibular cartilage, 

 which is a short, stout rod articulated with a large facet on 

 the side of the auditory capsule, and a longer, more slender, 

 ceratohyal cartilage, which passes forwards and inwards 

 from the hyomandibular to join a median plate, the basihyal 

 cartilage, in the floor of the mouth. The remaining five 

 arches are the branchial arches. 



23 



