GADUS 71 



and hyoid) is somewhat modified. In the dogfish, the palato- 

 ptery go- quadrate cartilage forms the margin to the upper jaw, 

 but in the bony fish this is no longer the case. Here 

 it is formed by the paired premaxilla and maxilla. Lying 

 median to these are the paired palatine (which touches the 

 brain-case), the three pterygoids (ecto-, endo-, and meta- 

 pterygoid), and, farther back, the quadrate. These bones 

 arise in relation to the palato-quadrate arch, and they therefore 

 no longer form the upper boundary to the mouth, but lie at 

 the sides of its roof. The quadrate articulates with a bone 

 of the lower jaw called the articular, and which corresponds to 

 Meckel's cartilage in the dogfish. Here again a new margin 

 to the jaw is formed, by the dentary. The ventro-posterior 

 part of the lower jaw is formed by the angular. 



The suspension of the jaws is hyostylic, i.e. the quadrate 

 is connected with the neurocranium by the hyoid arch. The 

 hyoid-arch skeleton consists of an upper hyomandibula which 

 articulates above with the auditory capsule, and is pierced by 

 a foramen for the hyomandibular branch of the facial nerve. 

 Beneath the hyomandibula is the symplectic to which the 

 quadrate is attached. The ventral portion of the arch is made 

 up of the epihyal, ceratohyal, and hypohyal. The epihyal is 

 connected with the symplectic by the interhyal. Below and 

 between the hypohyals is a median basihyal. The ceratohyal 

 bears branchiostegal rays. 



The operculum is a posterior extension of the hyoid arch, 

 and it is supported by four bones which are fixed on to the 

 hind edge of the hyomandibula and symplectic. These are 

 the preopercular, opercular, sub-, and interopercular bones. 



Pectoral Girdle. — The primitive girdle corresponding to 

 that of the dogfish is formed by a dorsal scapula and a ventral 

 coracoid, on each side. Here they are ossified. With these 

 the pectoral fin articulates by means of the radials. These 

 radials are short and fused, and the web of the fin is supported 

 by the lepidotrichia. Another series of bones is plastered 

 on to this primitive girdle from in front. These bones are 

 the cleithrum, post-cleithrum and supra-cleithrum. The 

 supra-cleithrum articulates with the post-temporal so that the 



