14 



SALMONID^ OV BRITAIN". 



this is a very noteworthy fact, as in some instances in which there exists a 

 discrepancy in the acconnts of two authors as to the shape of this fin, such may 

 be owing, not to an error in facts, but to a difference in the method in which the 

 examination was conducted. 



Fig. 6. Caudal fin of a sea trout, expanded half and two-thirds. 



Locomotion is the main use to which the fins of fishes are put, but even in 

 locomotion other forces are frequently or rather generally brought into play to 

 assist the fins, whether such is for the purpose of swimming, or for leaping as in 

 the salmon Avhile ascending rapids when the muscles of the tail are of great 

 assistance. 



The skeleton* or endo- 

 skeleton of Salmonoids, 

 consists essentially of a 

 skull and a vertebral or 

 spinal column (to which 

 are certain appendages) 

 these forming a protection 

 to the cerebro-spiual ner- 

 vous system and large 

 blood-vessels present in 

 the long axis of the body. 

 The vertebra3, of which 

 the spinef is made wp, 

 consist of a varying num- 

 ber of bones, the bodies of 

 each of which are excavated 



^^ 



at either end causing them 

 to be bi-concave or amphi- 

 coelous. The cavity pro- 

 duced by the apposition of 

 the two concave surfaces is 

 filled up with gelatinous 

 substance the remains of 

 the notochoi'd, while it is 

 covered in by connecting 

 ligaments. Consequently, 

 between the vertebrte are 

 elastic balls of semifluid 

 consistence which enables 

 them to move freely one 

 upon another. 



Fig. 7. Section of two caudal 

 vcrtebrffi of a salmon, c. cen- 

 trum : ha, hremal arch : 7(.s. 

 haemal spine : na, neural arch : 

 7is. neural spine. 



* The numerals employed for the various bones in this work are almost identical with those 

 of Cuvier and Owen, being as follows : — 1, Frontal. 2, Prefontal. 3 (Ethmoidc, Cuv.), Nasal. 

 4, Postfrontal. 5 {lldsilairc, Cuv.), Basioccipital. G (.S>/ic'«o;(?ep-/HC?>(/, Cuv.), Basisphenoid. 

 7, Parietal. S {Interparietal ou Occipital siqjericur, Cuv.), supra-occipital. 9 {Occipital exicriie, 

 Cuv.), Paroccipital. 10 {Occipital lateral, Cuv.), Exoccipital. 11, Alisphcnoid. 12, Mastoid. 

 13 {llocher, Cuv.), Petrosal and Otostcal. 14, Orbitosphenoid. 15 {SpJicm'ide antcrieur, Cuv., 

 Ethmoid and Ethmoturhinal, Owen), Basisphcnoid (Huxley). 16, VOmer. 17 {Intcnita.villairf, 

 Cuv.), Prcmaxillary. 18, Maxillary. 19 {Sous-orbitairc, Cuv.), Infraorbital ring. 20 {Nasal, Cuv.), 

 Turbinal. 22, Palatine. 23 {Temporal, Cuvier, Epitympanic, Owen), Hyomandibular (Huxley). 



