a4 
THE MARSIPOBRANCHII. 193 
II. Huxley, in a classical monograph on the subject, 
has shown* that the sub-ocular skeletal arch (Pl. [X fig. 1 
p.q.) and the cartilages which he terms the ‘“‘ postero- 
lateral’? ones (l.) (the ‘“‘ Zweite Seitenplatte’’ of Joh. 
Muller)+ answer in all essential respects to the parts of 
the cartilaginous mandibular arch of other vertebrata ; 
and he showed that these parts, together with those 
which support the sucking mouth of the adult Lamprey 
and of the Anuran Tadpole, admit of a detailed comparison, 
except (p. 423) for the presumed absence in the former 
of an external maxillary ramus to the trigeminal nerve. 
He subsequently discovered the existence of this,t and 
thus proved that at any rate the Petromyzontoid family 
of the Marsipobranchii is a jaw-bearing one. 
The term ‘‘gnathostomata’’ is used indifferently, to 
express either the mere possession of jaws, apart from any 
consideration of teeth, or (and more generally) that of a 
dentigerous jaw apparatus. Ifthe former definition be ac- 
cepted, the Marsipobranchii must stand as gnathostomata ; 
and if the latter, the mere absence of calcified teeth in the 
adult will not justify their removal from the gnathostom- 
atous series, so long as forms like the Sturgeon, in which 
a similar modification is realized, are retained therein. 
III. The lowest living Sturiones (Polyodon) retain 
their teeth for life. The researches of Knoch§ and Parker|| 
have revealed the existence of formidable teeth on the larval _ 
jaws of Acipenser ruthenus. Seeing, therefore, that the 
calcified teeth of the higher Sturiones wholly disappear 
*Jour. Anat.and Phys. Vol. X, p. 412, 
at Loe: Cit. y Ps, LC 4. 
+Phil. Trans., 1883, pp. 414—415. It had been contemporaneously 
described by Fiirbringer in 1875 (Jenaisch. Zeitschr. Bd. IX, pp. 62—67). 
§ Bull. Soc. Imp. des Nat. Moscou. T. xliv, p. 281, 1871. 
|| Phil. Trans., 1882, p. 154, Pl. XIV, figs. 5, 6. 
