Explanation of Plate II 



Jaw muscles of Amia and Lepidosteus, representing the Ganoidei Holostei, and 

 of Anguilla, representing the Teleostei Apodes 



Fics. 1 and 2.— Amia. (Muscles mainly after Allis.) 



In the Holostei and Teleostei the adductor mandibular and levator maxillae 

 superioris of selachians are subdivided into numerous muscles all lying in 

 front of the hyomandibular and innervated by V a ; while the C. 2 sd. group 

 behind the hyomandibular, which is innervated by VII, includes three muscles 

 (Ad. hy., A. o., L. o.). The levator arcus palatini (L. a. p.) and the dilator 

 operculi (D. o.) belong to the C. x sd. series and appear to represent the pro- 

 tractor hyomandibularis of the sturgeon (PI. I, Fig. 3). The levator maxillae 

 superioris (L.m.s.) includes several slips of which only one is shown. The 

 first division of the adductor mandibular (Adm L ) covers the cheek behind the 

 eye and runs from the preoperculum to the mandible. The fourth division 

 (AdmJ is lodged in the Meckelian fossa of the mandible. The dilator operculi 

 (D.o.) passes through a groove or depression in the hyomandibular and is 

 inserted by tendon into the operculum. 



Fig. 3. — Lepidosteus. 



In correlation with the anteroposterior elongation of the head the jaw 

 muscles are nearly horizontal instead of vertical. This oblique insertion gives 

 great speed but low power in the closing of the jaw. The protractor hyomandib- 

 ularis (P. hy.), as in Acipenser (Plate I, Fig. 3), runs from behind the eye to 

 the anterior border of the hyomandibular. The second slip of the adductor is 

 now above the eye instead of behind it. 



Figs. 4 and 5. — Anguilla sp. 



In this peculiar teleost the adductor mandibular is greatly enlarged and has 

 spread out upon the top of the skull after the fashion of the capiti-mandib- 

 ularis of certain Amphibia. The large dilator (D.o.) and levator operculi 

 (L.o.) muscles assist in the strong respiratory movements of the branchial 

 region. 



