3S0 I>A VISON. [Vol. XI. 



part of the orbit, and therefore deserves the name quadrato- 

 jugal, as some authors have already called it. 



The mandible is a simple structure, each ramus being com- 

 posed of these bones, viz., the dentary, the angular, and ar- 

 ticulatory. The dentary supports twenty-two teeth, and forms 

 the whole external portion of the ramus, and appears for some 

 distance in front on the inner side. The external surface 

 presents a foramen for the mandibular nerve. The angular 

 and articular are so well coossified for the most part that their 

 boundaries cannot be clearly defined. Anterior to the facet 

 for articulation with the quadrate, the articular abruptly rises 

 into a prominence, to which the temporal muscle is attached. 

 The angular lies beneath the articular, and forms a projection 

 behind it, in which the digastric muscle is inserted. Immedi- 

 ately anterior to the condyle is a notch for the insertion of the 

 masseter muscle. The rami are not anchylosed in front, but 

 are held together by cartilage. 



The hyoid apparatus oi AmpJiiunia is quite unlike that of any 

 other Amphibian (Fig. XV). There is but one basibranchial 

 to which are joined two ceratobranchials bound by cartilage. 

 There are four epibranchials. The basihyal is cartilaginous, 

 as are also all the epibranchials except the first. The hypo- 

 hyals are very short, being scarcely more than one-half as long 

 as the basibranchial. The ceratohyals are longer than the 

 ceratobranchials. The few cartilaginous formations of the 

 skull not already described will be discussed later. 



The Limbs. 



The limb bones of AmpJiiuma are characteristic of reptilia 

 in some respects. The fore limb consists of a humerus, ulna, 

 and radius, carpus, metacarpus, and phalanges. These bones 

 are proportioned with reference to each other, as in mammalia. 

 The humerus of a specimen one metre long is about one centi- 

 metre long. Its head is of cartilage. Immediately below the 

 head, on the anterior side, is a prominence for the insertion of 

 the biceps muscle. The distal third of the shaft is slightly 

 flattened to afford a more advantageous surface for the articu- 



