124 LECTURE V. 



the Remora, the Ribband-fish (Cepola), the Uranoscopus scaber, the 

 Blennies, the Siluroids, and the Apodal Fishes, with the exception of 

 the Sand-lance, wliich differs from the Eels in having the epi-coracoids. 



That they belong to tlie system of hsemal or inferior vertebrate 

 arches, and make a transition from the enormously developed arch of 

 the occipital to the ordinary costal arches of the second and sub- 

 sequent abdominal vertebrae, is indicated by their functions arising 

 out of their muscular attachments. In the Carp two ' musculi quad- 

 rati,' arising from the coracoid, are inserted into the epi-coracoid ; one 

 entirely, the other partially, and this latter is continued backwards, 

 to be similarly implanted into the rib of the second abdominal ver- 

 tebra; similar but more delicate muscular bands, degenerating into 

 aponeuroses, pass to the succeeding ribs, which are thus drawn 

 forward by the protraction of the epi-coracoids, or haemapophyses of 

 the atlas. By this action an effect analogous to the expansion of the 

 thorax in Mammalia is produced, the air-bladder being permitted to 

 dilate by the augmented capacity of the abdomen. 



As the terminal segment (hand or foot) of a locomotive member is 

 the essential part, or the great aim, so to speak, of the development of 

 such radiated appendage, it is the first part to appear and the last to 

 disappear. It exists without intermediate segment in the ventral fins 

 of all fishes, and in the pectorals of some, e. g. the Rays, and 

 the Lepidosiren {fig. 27.) : in others there may be a carpal seg- 

 ment, as in the Lophius {fig. 40. 56), the antibrachial segment being 

 confluent with the arch : in most fishes both a carpal (56) and an anti- 

 brachial segment exist, as in the Cod {fig. 19. 54, 55) ; in Polypterus 

 a metacarpus makes its appearance : but in none is there a distinct 

 brachial segment or humerus, interjiosed between the anti-brachium 

 and the arch ; it is at best represented by some small, supplemental 

 third bone manifesting that relation very dubiously. 



The special homology of the pectoral fins of fishes with the fore 

 limbs of quadrupeds was indicated by Aristotle, and first definitely 

 pointed out in later times by Artedi, in 1735, who says, — " Ossa pec- 

 toris et ventris in piscibus reperiuntur ; suntque in piscibus spinosis : 

 1. Claviculfe ; 2. Sternum; 3. Scapulae, sen ossa quibus pinnae pec- 

 torales ad radicem affiguntur." {Partes Piscium, p. 39.) Geoffrey St. 

 Hilaire, who has devoted special Memoirs to the determination of the 

 bones of the pectoral fin, had no knowledge of the primary homology 

 of the pectoral fin as the radiated appendage of the inferior arch of a 

 cranial vertebra, or of its serial homology with the branchiostegal and 

 opercular fins. He consequently speaks of the junction of the basis 

 of the fin to the cranium as something very strange : — " Disposition 



