OSSEOUS SYSTEM. 193 



and being interposed in the above manner between two vertebrae, 

 constitutes an elastic apparatus, performing functions similar to 

 those of the intervertebral ligaments in Man ; it is formed partly 

 out of the remains of the chorda dorsalis and its sheath, as will be 

 pointed out more closely further on in speaking of the Cartilaginous 

 Fishes. The vertebrae frequently possess anterior oblique processes 

 (often absent) and posterior, which are rarely wanting ; both the 

 one and the other, however, can be but improperly compared with 

 the oblique processes of Man and the higher Vertebrata, seeing that 

 they are not united by articulating surfaces. The parts that, form 

 the arch of the vertebrae are continued into very large superior 

 spinous processes, which are well developed in Sparus, and still 

 more in Chaetodon, Pleuronectes, &c. ; but they are, on the con- 

 trary, low and depressed in the Anguilliform Fishes and in Lophius. 

 In Syngnathus the superior spinous processes of the vertebrae sup- 

 port the dorsal fins, and are divided into several widely radiating pieces. 

 The thoracic vertebrae are frequently provided with transverse apo- 

 physes directed somewhat downward : although they may be called 

 transverse processes, yet, judging from what we know of the develop- 

 mental history of the vertebrae, they must be essentially different 

 from those of the higher Vertebrata. They are frequently absent ; 

 when present they support ribs, but invariably project backward 

 and downward, where, converging, they coalesce to form the infe- 

 rior arches, which together constitute a canal, opposite to that of the 

 superior arches enclosing the spinal cord, and through which the 

 aorta passes. Upon the caudal vertebrae they support very large 

 inferior spinous processes. Occasionally, as in the Carp, Shad, 

 Pike, in Clupea, Zeus, Trigla, one or more ribless vertebrae, pro- 

 vided with peculiar processes, are situated in front of the costiferous 

 set, and are regarded as cervical vertebrae. Situated above and upon 

 the superior spinous processes, to which they are usually connected 

 by membrane to a greater or less extent, are the accessory or inter- 

 spinous bones, frequently of considerable size, and supporting supe- 

 riorly the rays of the fins. It is rare for the interspinous bones to 

 advance, as in Plagusia, far forward upon the skull, and form there 

 a crest. The fin-rays are in some instances, as in the Acantho- 

 pterygii, simple, pointed, horny spines, but in others, as the Mala- 

 copterygii, they are softer, divided several times at their extremity, 

 and transversely articulated ; they are united by ginglymus with the 

 interspinous bones, and it is between them that the membrane of 

 the dorsal fins is expanded. Perfectly similar interspinous and ray- 



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