62 MR. D, R. BHATTACHARYA ON THE 



conspicuous, dorsal elastic ligament (" ligamentum longitudinale 

 superius "), which runs longitudinally in the vertebral column at 

 the bases of the neural spines and above the spinal canal. 



Before proceeding further, T wish to ofl'er my sincere thanks to 

 Dr. Woodland for suggestions offered during the progress of my 

 work, and for assistance in the writing up of this paper for 

 publication, especially in connection with Section V. 



II. The Aortic Ligament in Pseudeutropius garua taken, 

 as a Type. 



I have selected the aortic ligament of Pseudeutropius garua as a 

 type for detailed description because this is well developed in this 

 species, because this fish is plentiful in the local bazaar, and 

 because the ossification of the vei-tebral column in this fish is not 

 so pronounced as in many other species, and so there is less 

 hindrance to proper decalcification of the vertebral column for 

 section-cutting purposes. 



1. The Disposition and Attachments of the Ligament. 



The aortic ligament in this fish is a comjjact band of highly 

 elastic tissue running longitudinally inside the doi'sal aorta. In 

 its fully formed condition, it appears to hang down into the 

 cavity of the aorta, suspended by a fold from the median dorsal 

 wall of the aorta (Plate II. fig. 7) — in fact, the suspending fold 

 surrounds the ligament in much the same way as the mesentery 

 surrounds the gut (text-fig. 4). Anterioi'ly, the major portion of 

 the ligament ends beneath the basioccipital bone. The ligament 

 pierces through the dorsal wall of the aorta, just at the point where 

 the most posterior efferent branchial vessels meet, and breaks up 

 into bundles of elastic fibres which become severally attached to 

 the basioccipital bone and give the whole structure a fan-shaped 

 appearance (text-fig. 1, a.f.s.). At this place there is generally 

 a pad of cartilaginous tissue developed. A small portion of the 

 ligament, however, after perforating the dorsal wall of the aorta, 

 runs anteriorly close beneath the basioccipital in the median line, 

 and, after dividing into two, runs beneath the parasphenoid bone 

 and becomes attached to the vomer by a series of branches. The 

 dissection here had to be done under the binocular microscope as 

 the branches were exceedingly fine and delicate. 



At the posterior end the ligament is attached to the hypural 

 bone, or rather the bone which I'epresents the fused urostyle and 

 the hypural, close to the point of junction of the latter with the 

 last vertebi'a. There is a definite concavity in the bone here, in 

 which cartilaginous tissue is developed. The ligament here also 

 spreads out and breaks up into smaller bundles of fibres, which 

 acquire a strong attachment with the bone (text-fig. 1, p.f.s.). A 

 small portion of the ligament runs posteiiorly for a short distance 

 and becomes attached to the middle region of the hypural bone. 



