VISCERAL SKELETON. 235 







below the post-orbital groove : its outer end 

 articulates with the lower segment of the arch 

 opposite the angle of the mouth. To its hinder 

 border are attached a series of rods of cartilage 

 gill-rays which support the gill-folds. 



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. 



Skulls, like that of the dog-fish, in which the 

 hyoidean arch forms the suspensorium of the 

 lower jaw, are spoken of as hyostylic. 



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-ravs 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 produced behind into two horns which 

 are attached by ligaments to the dorsal surfaces 

 of the ceratohyals. It is perforated by the neck 

 of the * thyroid gland.' 



3. The branchial arches are the remaining five visceral 

 arches : they diminish in size from before backwards, 

 and each is divided into four segments on each side. 



a. The pharyngo-branchials, the most dorsal elements, 



are flattened rods running forwards and outwards 

 in the roof of the pharynx. The anterior ones 

 are connected with their fellows of the opposite 

 side by ligament ; and the last two of each side 

 are much smaller than the others, and fused 

 together. 



b. The epi-branchials are short broad plates attached 



to the outer ends of the pharyngo-branchials. 



