226 



THE FROG— THE PLATANA 



2. Remove the skin from the roof of the mouth and note the parasphenoid, 

 a large ±-shaped bone occupjdng the ventral surface of the cranium, the paired 

 vomers bearing the vomerine teeth, the premaxillae, the maxillae, the slender 

 palatines, the triradiate pterygoids, the squamosals lying under the pterygoids, 

 the quadrato-jugals, the pro-otics, and the exoccipitals. {See Fig. 81, page 224.) 



[In the Platana there is only one vomer. The pterygoids are large and have leaf- 

 like processes, which are prodv£ed towards the middle line, and which cover the 

 Eustachian passages. There are two well-developed quadrates for the articulation 

 of the lower jaw ; and there is a basioccipital, composed of cartilage. The orbito- 

 sphenoid and the alisphenoid are well marked. The palatines are absent.^ 



Make a drawing of the ventral aspect of the skull. 



3. Make a drawing of the skull viewed from the side to show the premaxilla, 

 maxilla, quadrato-jugal, nasal, sphenethmoid, fronto-parietal, pterygoid, 

 squamosal, and pro-otic. 



[In the Platana the supra-ethmoid, orbitosphenoid, alisphenoid, extrastapedial, 

 and columella may be noted in addition.] 



Fronto-parietal 



Faraapbeooid 



Pro*otic 



Pterygpid 



Alispb.enoid 

 Fro-otic '■ Fronto-parietal 



Orbitpsplienoid 



Supraethmoid 



Ouadrato-juKBl 



Aneulo-splenial 



Dentary 



Extraatapediat 



Premaxilla 

 \ MakiUa Nasal 



' Pteryefoid Squamosal 



Mentome'ckellan 



Articular Dentary 



A B 



Fig. 82. — A. Side View of the Skull of Mana ; and B. of Xenopits. 



4. Remove the skin from the lower jaw, and make out the. bones replacing 

 the original Meckel's cartilage, viz. the mento-meckelian, dentary, and angulo- 

 splenial. 



[In the Platana the lower jaw is composed of the mento-meckelian, dentary, and 

 articular.] 



Make a drawing of the lower jaw. 



Nervous System. 



A. The Central Nervous System. 

 The Brain. 



Carefully remove the fronto-parietals so as to expose the brain and note the 

 following parts : — 



(a) The olfactory lobes, forming the most anterior portion of the brain, 



united together in the middle line. Anteriorly the olfactory nerves 

 are given off. 



(b) The cerebral hemispheres, a pair of smooth elongated bodies. 



(c) The thalamencephalon, Ijdng immediately behind the cerebral hemi- 



spheres. It is covered by the choroid plexus, a thick vascular 



