66 MR. D. R. BHATTACHARYA ON THE 



in order to take out the aorta intact for histological purposes. 

 These masses acquire a strong attachment with the connective 

 tissue of the vertebral column. Each of the big masses of con- 

 nective tissue lies beneath the body of a vertebra, and I have, 

 therefore, called it " sub-vertebral mass," in contradistinction to 

 the thinner layer of adventitia, which connects the adjoining big 

 masses and which I have referred to as '' sub-intervertebral 

 mass" because it lies beneath the intervertebral region of the 

 adjoining vertebrae (text-figs. 3 and A, con., con.'). These "ver- 

 tebral masses " of connective tissue are segmentally arranged in 

 relation to the vertebrae, for they are found beneath each vertebra 

 from the first to the last. These masses seem to serve as a 

 cushion or pad for the strong and tough elastic ligament. During 

 the lateral flexions of the body, in which the aorta also takes 

 part, the ligament though itself stationary is displaced from its 

 median position inside the aorta. But it is never allowed to go 

 beyond the range of these masses, and probably it never actually 

 touches the wall of the aorta. Thus the ligament is protected 

 from undue strain which would result from direct contact with 

 the vertebral column, since the aorta lies in close contact witli 

 its ventral surface. In the "sub-intervertebral" region the 

 adventitia layer of the ligament and the dorsal wall of the aorta 

 are much thinner (Plate I. fig. 2). But the aorta in this region 

 is more strongly attached to the connective tissue of the vertebral 

 column than in the " sub- vertebral " region. 



Microscopic examination of the transverse sections (text-fig. 4) 

 shows that the ligament lies in the middle coat or media of the 

 dorsal wall of the aorta, the intima being reflected over the pre- 

 lection of the ligament into the aorta lumen. Muscle-fibres are 

 practically altogether absent from the dorsal region of the aorta 

 wall (though smooth muscle-fibres are present in the latei'al and 

 ventral regions), and it is noteworthy that it is in this position 

 that the longitudinally-elastic ligament is situated. Outside the 

 ligamentous layer is the thick and stout adventitia layer, though 

 in between the two a thin layer of muscular fibres, elastic fibres, 

 and connective-tissue cells may generally be found (Plate II. 

 fig. 11). 



On a more minute examination of thin longitudinal and trans- 

 verse sections, under high power, the ligament seems to consist of 

 bundles or groups of elastic fibres (Plate II. fig. 11, bun.), both of 

 the finer and coarser varieties. The fibres branch and unite and 

 run longitudinally throughout the length of the aorta. Owing 

 to their extreme elasticity and to the fact that the fibres are so 

 thickly clustered as to give the impression that they are running 

 in definite bundles, they acquire a wavy shape towards the exposed 

 sides and especially near the cut ends of the ligament (Plate I. 

 fig. 2, Ug.). In a transverse section the bundles of the elastic 

 fibres of the ligament may generally be seen to lie transversely in 

 the lower or ventral portion of the ligament and more or less 

 vertically in the upper or dorsal portion of the ligament (Plate 11. 



