DESCRIPTIONS OF PREPARATIONS. 



is very large and dentigerous, and of a characteristic shape. The maxilla 

 (Mx.}, which is edentulous, lies behind and parallel to it, and does not form 

 the margin of the gape of the mouth. This disposition of the two bones is 

 nearly universal among Teleostei. The base of the cranium is underlaid by 

 two bones a single vomer ( F0.), dentigerous in front, and a parasphenoid 

 (P. 5.) which extends back to the basi-occipital. These two bones, as well 

 as the praemaxilla, maxilla, nasal, frontal and parietal are preformed in 

 membrane, the remainder belong to the cartilaginous cranium, which per- 

 sists as cartilage beneath the parietal and frontal regions. 



The jaw apparatus (Fig. 9) is very remarkable. It is connected to the 

 cranium in front by the palatine (Pa} and behind by the hyomandibular 



PM. 



Op. 



FIG. 9. From a specimen (natural size). 



(Hm.}. The palatine (Pa.} is dentigerous. There is a slender pterygoid (Pt.} 

 ( = ectopterygoid of Huxley), which bears a few teeth anteriorly and de- 

 scends along the anterior edge of the quadrate, while a thin plate-like meso- 

 pterygoid (M. Pt.} (= entopterygoid of Huxley) extends horizontally 

 inwards. These bones are formed in a bar of cartilage lying in front of the 

 mouth in the embryo. Another bar of cartilage Meckel's arch which lies 

 behind the mouth segments transversely. The upper, or proximal portion, 

 forms the metapterygoid (Mt. Pt.} and the quadrate (Qu.). The latter has 

 a rounded articular head for the articular element of the lower jaw, and 

 both bones are firmly united to the bones in front and behind them. The 

 lower or distal segment constitutes the lower jaw in part. Its upper end 



