VISCERAL SKELETON 209 



cartilage. Each rod is further divided into an upper 

 and a lower segment. 



a. The hyo-mandibular cartilage, or upper segment, is 



a short stout bar of cartilage, projecting almost 

 horizontally outwards from the skull, but slightly 

 downwards and backwards. Itaonner and upper 

 end articulates with a concave surface on the side 

 of the sTmll, near its hinder end, and immediately 

 below the post-orbital groove : its outer end arti- 

 culates with the lower segment of the arch, opposite 

 the angle of the mouth. To its hinder border are 

 attached a series of branching rods of cartilage 

 the gill-rays which support the gills. 



b, The cerato-hyal, or lower segment of the hyoidean 



arch, is a longer and more slender bar which runs 

 forwards and inwards in the floor of the mouth, 

 just behind the lower jaw, and partly overlapped 

 by it. It bears gill-rays along its posterior border. 



c, The basi-hyal is a broad median plate of cartilage, 



lying in the floor of the mouth behind the lower 

 jaw. It is rounded anteriorly, and produced 

 behind into two horns which are attached by 

 ligaments to the dorsal surfaces of the cerato- 

 hyals. 



d. The suspensory ligaments of the jaws may be con- 



veniently considered here. 

 '. A strong pre-spiracular ligament, in which is 

 a small nodule of cartilage, runs from the ante- 

 rior border of the auditory capsule to the distal end 

 of the hyo-mandibular cartilage, where it blends 

 with ligaments connecting the hyo-mandibular 

 cartilage 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. 



The hyo-mandibular cartilage in the dog-fish 

 is spoken of as the suspensorium, because it forms 

 the skeletal link between the jaws and the skull. 



