VISCERAL SKELETON 211 



The third and succeeding hoops are more slender : they 

 surround the pharynx and support the gills. 



To see the visceral skeleton properly, a roll of paper should 

 be passed in at the mouth-opeping, and hack through the 

 several hoops. 



1. The first or mandibular arch is very greatly modified ; 

 its dorsal part is represented by the pre-spiracular 

 ligament, while its ventral part is large and stout 

 and forms the lower jaw. The upper jaw is formed 

 as an outgrowth from its anterior edge. 

 a. The pre-spiracular ligament is a strong fibrous 

 band in which is a small nodule of cartilage, and 

 which runs from the anterior border of the 

 auditory capsule to the distal end of the hyo- 

 mandibular cartilage, where it blends with 

 ligaments connecting the hyo-mandibular carti- 

 lage with the upper and lower jaws, close to the 

 angle of the mouth. An additional ligament 

 connects the lower jaw with the cerato-hyal a 

 short way below the angle of the mouth. 

 1). The upper j aw consists of a pair of stout cartilaginous 

 rods, wide behind and narrowing towards their 

 anterior ends, where they are united across the 

 middle line by ligament. They extend forwards 

 as far as the openings of the olfactory capsules, and 

 are connected by stout ethmo-palatine ligaments 

 with the base of the skull, at the antero-inferior 

 angles of the orbits. They bear teeth along the 

 ventral border of the anterior two-thirds of their 

 length. 

 c. The lower jaw consists of a pair of wide flattened 

 bars of cartilage, which are movably hinged with 

 the upper jaw behind, and bound together by a 

 median ligament in front. It lies, when the mouth 

 is shut, parallel to and immediately behind the 

 upper jaw. It bears teeth along the dorsal border 

 of the anterior two-thirds of its length on each 

 side. 



p 2 



