74 MR. D. R. BHATTACHARYA ON THE 



evident that though the ligament is well developed in the Silurid<i& 

 (a primitive group), yet it cannot be regarded as a primitive 

 structure, seeing that it is not developed in many other primitive 

 groups of fishes. 



As regards the development of the ligament, I have not been 

 able to study this for lack of material. It is, however, evident 

 that the ligament must arise as a special development of the 

 inner dorsal wall of the aorta (Plate II. figs. 12, 13, 14), the elastic 

 fibres of the middle and inner coats of the aorta becoming 

 aggregated to form the continuous elastic ligament. This view 

 is borne out by the fact that in the " sub-intervertebral " regions 

 of the aorta in Rita huchanani (Plate I, fig. 4), and also at the 

 anterior and posterior ends of the aorta, the ligament pierces 

 through its dorsal wall and runs through the middle coat of the 

 aorta for some distance. 



Appendix: Methods of Preparation of Material. 



The marine specimens were fixed in 4 per cent, formalin, and 

 the fresh-water specimens, which were available locally, were 

 fixed in Potassium bichromate solution. The smaller specimens 

 were decalcified in a solution of 3 per cent, nitric acid in 70 per 

 cent, alcohol, which was changed every alternate day for from 3-5 

 weeks. Portions of trunk and tail region Avere imbedded in hard 

 wax and sections 8 jx thick were cut. The sections were stained 

 on the slide, mostly in Delafield's Ha?matoxylin, though I have 

 also, at times, used Borax Carmine and Picro-indigo-carmine for 

 diflferential staining with remarkably good results. 



EXPLANATION OP THE PLATES. 

 Plate I. 



Fig. 1. Dorsal aorta of Glorias magur (X 25). Note tlie absence of aiij-^ trace of 

 a ligamentous structure in the dorsal wall of the aorta, c.aor., cavity 

 of aorta ; d.w.a., dorsal wall of aorta. 



Fig. 2. Longitudinal section through the vertebral column and dorsal aorta of 

 JS^ltropiicktJrl/s vacJia in the caudal region, showing the relative positions 

 of the .dorsal ligament and the aortic ligament (X 5). The aortic 

 ligament in the caudal region is more closely attached to the dorsal wall 

 of the aorta than in the trunk-region, d.lic/., dorsal ligament ; sp.c, 

 spinal cord ; d.w.a., dorsal wall of aorta ; lig., aortic ligament ; v.w.a.^ 

 ventral wall of aorta ; cav.a., cavity of aorta ; s.v.m., sub-vertebral mass 

 of connective tissue. 



Fig. 3. Transverse section through the sub-vertebral region of the dorsal aorta in 

 Bita huchanani (X 16). car., cartilaginous tissue ; lig., aortic ligament. 



Fig. 4. Transverse section through the sub-intervertebral region of the dorsal aorta 

 in Rita huchanani (X 16). lig., aortic ligament. 



Fig. 5. Anterior termination of the aorticligament in Sihmdia gangetica (X i nat. 

 size), aor., dorsal aorta; lig., aortic ligament; a., anterior position of 

 aortic ligament which, passing through the dorsal wall of the aorta, 

 becomes attached to the basioccipital bone ; c, the point of origin of the 

 anterior branch of the ligament after it perforates the aorta; 6., basi- 

 occipital ; par., parasphenoid ; a.lig., anterior branch of the ligament ;■ 

 a., the iibres of the ligament which spread out to form a thin sheet. 



Fig. 6. Ventral view of the skull and anterior vertebraj in Wallago attu (nat. 

 size), par., parasphenoid; &rts.o., basioccipital ; 1st v., first vertebra;. 

 p.t., post-temporal ; 27id v. second vertebra. 



