20 



VERTEBRATE RESPIRATION 



Species to species: the following account is based mainly upon 

 the cod.* The functional relationships of the skeleton and 

 muscles are illustrated diagrammatically in fig. 6. 



As has been pointed out, the distinction between expiration 

 and inspiration is not clear in fish because instead of tidal ventila- 

 tion the water flows continuously across the respiratory epithe- 

 lium. It is most convenient therefore to describe the functional 

 system in terms of the muscles which alter the volume of the 

 buccal and opercular cavities. Expansion of the buccal cavity 



Fig. 6. 



Diagram to show the position of the main muscles involved in 

 respiration of an idealised teleost fish. The arrows point away from 

 the insertion which normally moves. Dotted muscles lie beneath the 

 skeleton. Muscles are numbered as follows: 1^~* adductor mandi- 

 bulae (four parts); 3 levator arcus palatini; 5^-^ dilator operculi; 

 6, levator operculi; 7 adductor hyomandibulae; 7^, adductor arcus 

 palatini; 8 adductor operculi; 9, hyohyoideus dorsalis; 10, hyohyoi- 

 deus ventralis; 11, protractor hyoidei (geniohyoideus) ; 31-34, 

 adductors of branchial arches. 37, sternohyoideus. 



Pmx, premaxilla; Mx, maxilla; LJ, lower jaw; Hmd, hyomandi- 

 bular; Op, opercular; R, branchiostegal rays; CI, cleithrum; Mx-Md 

 Lig, maxillo-mandibular ligament. (After Hughes and Shelton, 1962.) 



* For a detailed description of the skeleton and muscles, see Saunders 

 and Manton, Practical Vertebrate Morphology, 3rd Edition. Oxford 

 University Press, 1959. 



