188 SIREN. 



branchiate Batrachians which stand at the lowest step of the Reptilian 

 Class, and not only the superior maxillary teeth, but the bones 

 themselves are absent in the Siren, Menobranchus and Proteus. 



76. Siren. — In the Siren (/Siren Zacer^ma, Linn.) the lower margin 

 of the intermaxillary bones, and the sloping anterior and upper margin 

 ofthe lower jaw are trenchant, and are each encased in a sheath of firm 

 albuminous, minutely fibrous tissue, harder than horn, (PL 62, 

 fig. 1). The bones thus armed slide upon each other like the blades of a 

 pair of curved scissors, when the mouth is closed, and are well adapted 

 for dividing the bodies of small fish, aquatic larvae, worms, &c. 

 The horny substitute for teeth on the lower jaw is supported by 

 the bony element corresponding with the premandibular of the 

 jepidosiren and other fishes. A second osseous piece, appUed to the 

 inner surface of the ramus of the jaw, and representing the splenial 

 or opercular element in the jaw of the crocodile, is beset with 

 numerous minute pointed teeth, arranged in short oblique rows, and 

 directed obliquely backwards. The palatal surface of the mouth pre- 

 sents on each side two flat, thin and moderately broad bones, forming 

 an apparently single oblique oval plate, which converges to meet its 

 fellow at the anterior part of the palate, so as conjointly to constitute 

 a broad rasp-like surface in the form of a chevron, (PL 62, fig. 2). 



The anterior long plate on each side, which may be regarded 

 as the representative of the divided vomer, supports six or seven 

 obhque rows of small pointed retroverted teeth ; the smaller pos- 

 terior plate, probably the homologue of the pterygoid, is beset 

 with four rows of similar teeth : there being thus ten or eleven 

 rows on each side of the palatal chevron. The number of den- 

 ticles in the middle rows is eleven or twelve ; they become fewer 

 in the anterior and posterior rows : they are all of similar size and 

 form, corresponding with those of the lower jaw to which they are 

 opposed. 



The condition of the dental system in this, the lowest of the class 

 of reptiles, is not without interest independently of the absence of 

 the superior maxillary teeth, and of the presence of the palatal and 

 inferior maxillary ' dents en cardes.' If, for example, the dense sheath 

 of the trenchant anterior parts of the upper and lower jaws had 



