132 LECTURE VI. 



jaw. This process corresponds with the outAvard and downward 

 prolongation of the transversely developed pre-niaxillary in Osseous 

 Fishes. 



The maxillary bone (ib. 2l) is a small and simple oblong plate, 

 articulated to the under part of the base of the outer process of the 

 pre-raaxillary, and attached by the whole of its inner and posterior 

 side to the palatine. Only the gradual transmutation of the similarly 

 insignificant ' os mystaceum ' in the Osseous Fishes to its higher 

 form and functions in the Salmonoid and Salamandroid species, could 

 have made the homology of this separate bone appreciable in the 

 Sturgeon. 



The OS palati (ih. 20) articulates by its anterior angle with both 

 maxillary and pre-maxillary ; expands postei'iorly in one direction 

 towards the median line, along which a slender pointed process is 

 directed forwards ; and in the opposite direction outwards and 

 downwards to the inner side of the cartilaginous joint of the lower 

 jaw ; like the pterygoid extension of the same part of the arch in the 

 Lepidosiren. A slender ossicle {ib. 74) extends along the outer 

 side of the cartilaginous joint, from the end of the premaxillary 

 process to the posterior ridge of the palatine bone ; homologous 

 with the angulo-labial cartilage in the Squatina. In the cartilagi- 

 nous interspace between the anterior notch of the palatines and the 

 premaxillary synchondrosis, I have found a small separate ossification 

 in a very large and old Accipenser Sturio. 



The roof of the mouth is extended posteriorly by three cartilagi- 

 nous plates : one single {ib. 20 a) and extending backwards, from the 

 j)osterior interspace of the palatines ; this seems to be the homologue 

 of the two median cartilages, called ' palatal ' by Dr. Henle, on the 

 roof of the broader mouth of the i\^a/'c//?e* : the two outer cartilages 

 correspond with those called ' ptei'ygoid ' by the same author in the 

 same Brazilian Torpedo, f 



The lower jaw («6. 32), which is joined by a concavity to the 

 trochlear cartilage supported by the pterygoid process of the palatine 

 and the premaxillary, consists pi'incipally of a single bony ramus on 

 each side, joined by ligament to its fellow at the symphysis, with a 

 posterior excavation filled by cartilage, in which there is a small 

 detached ossification in the old Accipenser Sturio above adverted 

 to.J 



The whole of the above apparatus of the jaws is suspended to 



* IMiiller's IMyxinoiden, tab. v. fig. 3 and 4. e e. -1- lb. d d. 



\ The bones and gristles of the Sturgeon's mouth are well described by J. 

 Miiller (xxi.); but ichthyotomically, i. e. without determination of homologies, and 

 accordingly under special names. 



