302 FISHES. 



We find frequently interspinal bones (No. 76) without rays, and 

 sometimes also we see them supporting more than one. The form of 

 this bone is nearly that of a four edged poinard, the point being buried 

 in the muscles, and the handle on a level with the skin supporting 

 the external ray. The part which supports the ray, has a transverse 

 suture, which sends off from it a sort of epiphysis (a. a.). This epi- 

 physis in several species produces a small point which passes into the 

 articulation of the succeeding ray, 



The interspinals are usually placed so that their points penetrate 

 between the spinous apophyses of the vertebrae, and each point is 

 attached by a ligamentous membrane before the extremity of one of 

 these apophyses ; but there are fishes, for example the pleuronectes, 

 and for the anal fin, the silures, &c, in which we find two small 

 bones for one vertebral apophysis, and others in which even these 

 conditions are not regular. 



It should be also observed that in many genera, such as the eels, 

 the ophicephales and the gymnotes, the inferior interspinals are 

 separated from the vertebrae by the cavity of the abdomen, which is 

 prolonged above the anal fin ; that in others, as in the pleuronectes, 

 they are to be found as far up as the head. These circumstances, 

 together with the fact, that in the parts of the back or tail which do 

 not support vertical fins, there are usually no interspinal small bones 

 although there are vertebrae, oppose our considering these bones 

 as forming a part of the vertebrae, or dismemberments of vertebrae.* 



The rays of the vertical fins (Nos. 74, 75) are articulated, each by 

 a loose gynglimus, with an interspinal small bone. For this purpose 

 their basis is generally divided into two small branches, each termi- 

 nated by an articular tubercle, which enters into the lateral depression 

 of the head of the interspinal small bone ; between these two tuber- 

 cles there is a small globular bone, on which the ray moves in two 

 directions ; but in the vertical plane their movement is more exten- 

 sive ; they can be elevated or laid backwards, thus raising the fin or 

 diminishing its height. Sometimes these two branches are again 

 joined below, and thus form a transverse ring, which entwines with 

 a longitudinal ring of the interspinal, as may be seen in Nos. 76, 77- 



A part of these vertical rays are pointed bones ; they are called 

 needles or spinous rays ; the bases only of the others are bony and 

 solid ; but the rest of their length is made up of a multitude of little 



* M. Geoffroy, (Memoirs of the Museum vol. ix. p. 97) thinks he has established 

 that, the superior spinous apophysis of mammalia, which he calls epial, and which 

 he supposes to be divided laterally into two parts, produces in fishes the interspinal 

 small bone and the ray, because its two parts ascend one on the other: he employs 

 the same reasoning with regard to the inferior rays, which he derives from the 

 spinous prominence of the small bone en chevron from under the tail of mammalia; 

 this small bone he calls cutaal. But, independently of the other singularities of these 

 views, the plaice which he took for example, was precisely the fish best calculated to 

 set him right ; for it has for each vertebra, two small inter-spinals, and two rays, 

 and even the first vertebra of the tail, aided by the post-abdominal bone, attached in 

 front of its inferior apophysis supports eight small bones and eleven rays of the fin of 

 the anus : this may be seen in Duhamel, part II. sect 9, pi. 12. Another argument 

 of equal weight against this system, is that every spinous or articulated ray is itself 

 divisible into two halves, one on each side ; whilst every interspinal is divided into 

 two pieces, one superior, the other inferior. 



