THE OSTEOLOGY OF AMIURUS CATUS. 285 



bone, lies the cartilaginous symplectic, in a perfectly dried skull, the 

 fossa being empty and an interspace occurring between the quad- 

 rate and the hyomandibular. The posterior border of the quadrate 

 is contained in a groove on the preopercidum ; behind and above it 

 articulates with the hyomandibular ; and above and in front with the 

 metapterygoid. 

 7. The Mandible, (PI. II., Fig. 1, Mn.) 



Consists of two portions, one on either side, united in the median 

 line in front by ligament. Each portion again consists of four parts. 

 These are as follows : — 



(a) The dentary, constituting the anterior two-thirds of the bone 

 and bearing numerous teeth. It is broader in front than behind, the 

 teeth being arranged correspondingly, there being 5-6 rows anteriorly, 

 tapering off to two rows posteriorly. The bone increases in height 

 posteriorly, and is grooved on the inner surface for the reception of 

 Meckel's cartilage and the articulare. The under surface presents 

 six pores, openings for branches of the mucous canal which runs 

 in this portion of the bone. 



(b) The articidare forming the posterior high portion of the bone, 

 and presenting the articular surface for the quadrate. It encloses 

 Meckel's cartilage posteriorly. 



(c) Meckel's cartilage, the remains of the primordial cartilaginous 

 mandible. It consists of a rod of cartilage lying on the inner sur- 

 faces of the dentary and articulare, its posterior portion being in- 

 cluded within the latter. 



(d) The angular e, fused completely with the articulare, being 

 merely indicated as a small triangular nodule below the articular 

 surface. 



The great size of the intermaxillaries and the limitation of the 

 teeth to them, as far as concerns the upper jaw, are points worthy 

 of notice. This is, of course, due to the specialization of the 

 maxillae for another purpose ; with the decrease in size of the lat- 

 ter was an increase of the former. The intermaxillse belong to that 

 class of bones which are formed by the fusion of cement-plates of 

 teeth. At first they are represented by a thin lamella of bone-bear- 

 ing teeth, but by means of osteoblasts the ossification extends into 

 the superjacent tissue in the form of trabecular which are, in their 

 histological details, similar to the cement plates. 



