272 



Appendices to Fifth Annual fieport 



of the fourth ; the third is three-fourths or more of the length of the 

 fourth, and the second about one-half its length. 



At the posterior end the last interspinous bone is short and somewhat 

 modified, and there passes backward from it a bony strip lying horizon- 

 tally, and about 3 mm. long in the adult fish, giving attachment to, and 

 evidently being an ossification of, the ligamentous end of the muscle. 



These interspinous bones do not symmetrically hold the position which 

 their name implies. In most cases, the 19 interspinous bones are 

 found to cover an interval (at their ventral ends) of only about 13 

 neural spines (about the 18th to the 31st). While the posterior bones 

 are fairly regular in their position, and in the circumstance that they run 

 in between the neural spines, the posterior four or five generally lying two 

 in each interneural space; further forwards there comes to be only one 

 interspinous bone to each interneural, and the anterior interspinous seldom 

 reach or just touch the tip of the neural spines. 



In regular interspinous position, however, there occurs a series of small 

 bones anterior to the dorsal fin, and extending forwards from it to the head 

 (PI. XV. fig. 1). The first being anterior to the first neural spine, the suc- 

 ceeding ones being arranged in the median line with their distal (dorsal) 

 extremities attached to connective tissue close beneath the skin, and their 

 proximal ends passing down — each behind a neural spine. The first two or 

 three of these interspinous bones have a slightly expanded flattened head, 

 and though apparently homologous with the interspinous bones of the fin, 

 are otherwise of a simple rod-shaped form. They are not found posterior 

 to the dorsal fin. 



The description of the dorsal fin rays and interspinous supports will 

 apply equally to the anal fin. There are generally 16 or 17 (an additional 

 minute one being generally present) rays in it, consisting of a very short 

 first ray, a second nearly as long as the third, behind which they shorten 

 again to the last, although not to such a marked degree as do the dorsal rays. 

 The last and penultimate rays are peculiar, in that to superficial examination 

 they appear to consist of a single ray more expanded distally than the others, 

 — they however are distinct rays, but their roots are always more closely 

 approximated to one another than occurs with the others, and behind 

 them there is a similar little ossification to that found behind the dorsal 

 fin. The interspinous bones again hold a pretty constant distance to each 

 other, and do so also with respect to the haemal spines in a more 

 marked degree than do the dorsals — the 17 or 18 interspinous bones 

 occupying the space of about 9 or 10 haemal spines, each interspinous 

 space therefore receiving as a rule a pair of interspinous bones. The 

 interspinous bones and rays are similar to and articulate in the same 

 manner as the dorsal, except that they are not provided with the bony 

 expansions found in the anterior dorsals. It is seldom that an inter- 

 spinous bone is distinctly developed for the anterior ray, and the first two 

 or three interspinous bones have not the distinct head found in the others. 

 In the young fish the rays are found ossified before their interspinous 

 supports, and when the latter are still cartilaginous. 



The Paired Pins. 



The pectoral girdle (PI. XVIII. figs. 26, 27) has been described by 

 Parker, and my examination of it modifies his description only in one or two 

 minor details. It consists of a strong curved clavicular bone (cl.), the 

 apex of which is bent slightly backwards; while the main stem curves gently 

 forward, and terminates anteriorly in a narrow hook-shaped process (cl.h.), 



