37 



PLATE XIX. 



TH.B . FROG" continued. 



SKELETON. 



%* The colours in left-hand corner of Plate refer only to SkulL 

 THE BONY SKULL- 

 FIG. 1. DORSAL VIEW 



Exoccipitals (L. ex, out ; occiput, the back of the head). 

 Pro-otics (Or. pro, in front of ; ous, otos, the ear). 

 Parietals (L. paries, a wall) . . ) 

 Frontals (L. front, the forehead) } unlte 

 Nasals. 



Premaxillte (L. prce, before ; maxilla, the upper jaw). 

 FIG. 2. VENTRAL VIEW, lower jaw removed 

 Parasphen'oid (Gr. sphen, a wedge). 

 Sphenethmoid or girdle-bone. 

 Voniers with teeth. 

 Premaxillas with teeth. 

 Pterygoids (Gr. pteron, a wiug). 

 Palatines, slender palate bones. 

 FIG. 3. SIDE VIEW 

 Squamosals. 

 Quadra to-j ugals. 

 Maxillae with teeth. 

 PremaxillDe with teeth. 



Mandible or lower jaw, consisting of two raini (L. ramus, a branch) without teetli. 

 f Meckel's cartilage forming the core. 

 ) Angulo-splenial . . ) . 



j Dentary without teeth j lnvestln S Meckel's cartilage. 



V, Mento-Meckelian bone (L. mentum, the chin), the ossified tip of Meckel's cartilage. 

 FIG. 4. POSTERIOR VIEW 



Exoccipitals with condyles (Gr. kondulos, a knuckle) for articulation' with vertebral column. 

 Foramen magnum (L. great opening), through which spinal cord passes into brain. 

 THE CARTILAGINOUS SKULL 

 FIG. 5. DORSAL VIEW 



Sphenethmoid bone, replacing cartilage and partly covered by the frontala (see fig. 1). 

 Nasal roof covered by nasals. 

 Fontanelles, membranous portions. 

 FIG. 6. VENTRAL VIEW 

 Sphenethmoid bone. 



Nasal floor anterior to Sphenethmoid covered by vomers. 

 Floor posterior to Sphenethmoid from the exoccipitals covered by the parasphenoid, which partly 



overlaps Sphenethmoid. 



Pterygoid bar, replaced by pterygoid and palatine bones (see fig. 2). 

 FIGS. 5, 6. MANDIBULAR SUSPENSORIUM, connecting lower jaw with skull 

 Posterior end articulating with Meckel's cartilage. 



Anterior end dividing j" Dorsal process or eras attached to outer wall of skull. 

 into ( Ventral process or eras continuous with pterygoid bar. 



. Two kinds of bone are distinguished in the skull according to their mode of origin 



1. Cartilage bones (red), as the name denotes, are first modelled in cartilage. 



2. Membrane or splint bones (blue) are those not so preformed in cartilage. 



