AORTIC LIGAMENT IN INDIAN FISHES. 67 



fig. 11, Ug.). This arrangement seems to be fairly constant 

 throughout the length of the ligament. 



III. The Ligament in other Fishes. 



The ligament in a transverse section looks either circular (e. g. 

 in Notopterus chitala, Laheo diplostomus, and Macrones aor) or 

 oval (e. g. in JSiitrojnichthi/s vacha, Rita bicchanani, and Engraulis 

 telara) or crescent-shaped (e. g. in Chatoessus manniinna^ Clupea 

 ■sindeiisis Clupea ilisha). The tsuspensory fold of the ligament 

 consists of a double layer of intima with a mass of connective 

 tissue in between. This mass of connective tissue may be very 

 thick, so as to give rise to round or oval masses — the " sub- 

 vertebral " masses (e. g. in Pseudeutropius garua, EiUropiiichthys 

 vacha)., or it may be thin (e. g. in Callichrous macrophthahmis _ 

 Callichrous pahda, Barhus sarana). Sometimes the suspending 

 fold is so thin and elongated that in a transverse section it looks 

 like the " neck " of the ligament (text-fig. 4, n.). In some cases, 

 the suspending fold is so deep in the trunk-region that the 

 ligament comes to lie quite close to the ventral wall of the aorta. 

 In such cases (text-fig. 3) in the " sub-vertebral " region the 

 ligament with its suspensory fold and connective tissue fills up 

 more than half the cavity of the aorta. The "neck" of the 

 ligament is thinner in the " sub-intervertebral " region than in 

 the "sub-vertebral" region (text-fig. 4). In some cases there is 

 no suspending fold in the " sub-intervei-tebral " region and the 

 ligament is developed in the wall of the aorta, and in a transverse 

 .section looks like a small protuberance (e. g. in Rita huchanani, 

 Plate I. fig. 4, Ug.). Dorsally to the suspensory fold or the neck 

 of the ligament there is always either a thinner or more generally 

 a thicker layer of connective tissue or a.dventitia. In some cases 

 (e. g. in Chatoesstts manminiia and Rita huchanani) a cartilaginous 

 pad is developed in this layer in the " sub- vertebral " region 

 (Plate I. fig. 3). 



In the majority of cases the ligament ends in the basioccipital 

 bone. In some the greater portion of the ligament becomes 

 attached to the basioccipital bone, but a small branch pierces 

 through the dorsal wall of the most anterior region of the aorta 

 and runs forwards to end in the vomer or parasphenoid bone 

 (e. g. in Etitropiichthys vacha., Pseudeutropius garua, Clupea ilisha, 

 ■Silundia gangetica). In others (e. g. in Macrones seenghala and 

 Catla buchanani) the ligament pierces through the dorsal wall of 

 the aorta a short distance behind its origin, and is attached to 

 the ventral side of the fused mass of anterior vertebrae. The 

 aorta here runs in close contact with and inside a bony groove 

 formed on the ventral side of the fused mass of anterior 

 vertebrae. 



In Wallago attu, in which the ligament is very well developed, 

 I have worked out in detail both by dissection under the binocular 

 microscope and by microtome sections the anterior termination of 



5* 



