* 



8 



teeth in a more or less advanced state, each of Avhich will 

 in its turn become fixed to the bone, by tlie successive shed- 

 ding of its predecessors. 



The jaws are moved by the following muscles : 



Action. 



1. Masseter (superficial temporal) a Flexor of the mandible. 



2. Temporal (deep) b do. 



3. Posttemporal c do. 



4. Tympano-mandibular d Extensor of the mandible. 



5. Costo andneuro-mandibulare ... do. 



6. Ectopterygoid,/ Depressor of the maxillary. 



7. Entopterygoid, ^ do. 



8. Postfrontopterygoid, h Erector of the maxillary. 



9. Presphenopterygoid, i do. 



10. Presphenopalatine, j Depressor of the maxillary. 



11. Presphenovomerine, k Depressor of the premaxillary 



1 2. Interraandibulary, I Attractor of the mandibles. 



13. Masto-tympanic Levator tympanici and ex- 



tensor of the mandible. 



14. Basispheno-tympanic Depressor tympanici and at- 



tractor of the mandible. 



15. Trachelo-tympanic Extensor of the mandible. 



Besides the primary actions given above, these muscles 

 have secondary actions in the attraction and devarication 

 of the mandibles, &;c. 



No written description of these muscles will convey such 

 a good idea of their situation and action as the figures in 

 Plates II, III and IV. I would only make a few remarks 

 on those which cannot well be figured. The prespheno- 

 vomerine is a thin tendinous muscle passing along the roof 

 of the mouth. The masto-tympanic is by no means easy 

 of discovery, and the basispheno-tympanic is, as a rule, only 

 to be found in venomous snakes. The muscle which I have 

 given as trachelo-tympanic is the trachelo-mastoid of Owen, 

 but as I always find it inserted into the tympanic, I prefer 

 the former name. 



