[83] THE OSTEO'LOGY OF AMIA CALVA. 829 



posterior elliptical facet described above, another bone of a conical 

 form, and about oue-half a centimeter long. This element seems to 

 take the place of the combined actinosts of the pectoral limb. Again, 

 the rays of the ventral fins are arranged in a peculiar manner ; these, 

 Avhich seem to number from seven to eight in an adult specimen, are 

 split as they are in the pectoral rays. The ends thus divided are held 

 well apart in order to allow the separate conical piece of bone to be in- 

 serted between them. As in the pectorals, too, these ventral fins are 

 " branched " as they approach their posterior terminations. In form 

 each fin is quite acute and the outer ray is the longest. 



Among the Teleosts the pelvic bones not only vary in position, but, as 

 we might readily imagine, vary almost iufinitely in regard to their rel- 

 ative size and shape. Indeed, it would be a difficult thing to convey 

 any adequate conception in such an essay as this, of these various forms. 

 They areas numerous, nearly, as the species themselves. These bones 

 are never attached to the vertebral column as we find them in verte- 

 brates above fishes. (Owen.) 



In Microptetnis salmoides they are represented by two separate and 

 symmetrical bones, that articulate with each other mesially, by their 

 inner edges. When thus united they form an elongated isosceles tri- 

 angle, with its apex held by ligament in the entering angle behind the 

 proscapulse. The outer borders develop a raised rim, and the planes 

 of the surfaces contributed by the two bones superiorly, on either side, 

 look upwards and outwards, the reverse being the case, of course, be- 

 neath. The postero external angles, as well as the hinder border, is 

 thickened and u^idulating for the articulations of the heads of the ven- 

 tral fin rays. There is, also, a characteristic process developed mesi- 

 ally on this border, into which each pelvic bone takes an equal share. 

 Above, it is bifid, being directed upwards and backwards, and com- 

 pressed anteroposteriorly ; below, it is peg-shaped and directed in the 

 same degree forwards and downwards. 



I fail to find any bony nodules, representing the actinosts, between 

 the ventral fin rays and the pelvic bones in this fish ; and the rays 

 themselves seem to be constructed upon the same plan as the pectoral 

 ones, being retained in their positions by firm ligaments and the skin. 

 The outer one, however, on either side, differs materially in form, being 

 spoon-shaped, with the 'concavity against the next ray on its inner side. 

 It also develops an inturned process, which curves over the next t^o or 

 three rays. This double arrangement seems designed to strengthen 

 the inner rays, and assist to keep them in their position. 



OF THE VERTEBRAL COLUMN, AND SKELETCN OF THE REMAINING- 



PARTS. 



EiGS. 14, 25, and 26. 



Among the general characters of this part of the skeleton we know 

 that " the vertebral column of fishes can only be divided into two re- 



