180 ANATOMY OF VERTEBRATES. 



a little bud attached to the skin of the belly, and from the fact 

 that all the fishes in the geological formations anterior to the 

 chalk are abdominal, that is, have the ventral fins near the pos- 

 terior end of the abdomen, as in the Sturgeon, fig. 29, v, we may 

 conclude that the supporting bones are, essentially, the haemapo- 

 physes of the last rib-bearing (or pelvic) abdominal vertebra. 

 Being suspended more or less freely from the under or ventral part 

 of the body, these fins are subject to great diversity of position in 

 relation to the two extremes of the abdomen. On these differences 

 Linnaeus based his primary classification of Fishes ; he united 

 together, for example, those fishes which have the pelvic or 

 ventral fins near the anus, fig. 29, to form the order called 'Pisces 

 Abdorninales ;' those with the ventral fins beneath the pectorals, 

 fig. 38, into an order called ' Pisces Thoracici ; ' and those with 

 the ventrals in advance of the pectorals, fig. 34, v, into an order 

 called ' Pisces Jugulares ; ' lastly, those fishes in which the ventral 

 fins were absent formed the order called ' Pisces Apodes] indicating 

 his recognition of the homology of such fins with the hinder or 

 lower limbs of higher animals. 



In the Sahnonidce (& Eriox, fig. 112, c) the ischia, 63, are 

 united by a cartilaginous symphysis at the medial line, and 

 underlie the last six abdominal vertebras. Each supports a 

 ventral fin of nine rays, 68. In the Angler {Lophius piscatorius) 

 the ischium is attached by one end to the coracoid, and expands 

 at the opposite end to join its fellow, and support the six rays of 

 the ventral. It also sends up a vertical process, simulating an 

 ilium. The ' thoracic ' character depends on the greater length of 

 the ischia, as compared with that in the 'jugular' fishes. In the 

 Lepidosiren, fig. 41, as in the Sturgeon, fig. 29, and other 

 ' ventral fishes,' the ischia, 64, are suspended beneath their proper 

 vertebra. They support in Lepidosiren a single-jointed ray, 66. 

 In Lepidopus, in the Blennies, the Forked Hake (Pliycis), the 

 Forked Beard {Raniceps), and some other fishes, the ventral fins 

 are likewise mere filamentary feelers. In the Lump-suckers 

 ( Cyclopterus), the ventrals unite together, and combine with part 

 of the pectorals to form a sucking disc or organ of adhesion, 

 below the head, just as the opercular and branchiostegal fins are 

 united together to form the gill-cover. The ventral fin is better 

 developed in the Plagiostomes than in other fishes. The support- 

 ing arch consists indeed of the same simple elements, haemapo- 

 physial, cartilaginous, confluent at the middle line, and loosely 

 suspended in the abdominal walls ; but they do not immediately 

 support the fin-rays. Two intermediate cartilages are articulated 

 to the expanded outer ends of the inverted arch ; the anterior is 



