156 
MR. MARSHALL ON THE DEVELOPMENT 
course of the lower part of this devious vein may vary; but above, it may always be 
identified as the enlarged azygos (originally the right cardinal vein*). 
3. The ti'unks of the right and left intercostal systems nearly equal. — The several 
modifications of this condition constitute the different varieties of so-called double 
vena azygos ; but although the azygos minor or hemi-azygos is in all these cases much 
enlarged by consolidation of its parts, yet it must be carefully discriminated from 
that true form of left vena azygos which exists, for example, in the Sheep, and in 
some animals having a left vena cava superior. 
а. In one set of these cases, the size and termination of the azygos vein itself being 
as usual, the azygos minor, enlarged and extending higher than ordinary, crosses 
over to the right side and joins the azygos vein near to or at its termination in the 
superior cava-l-, or ends in the upper cava itself:|:, or even it has been said in the right 
auricle'^. Most frequently, the azygos vein ending as usual, the enlarged azygos 
minor or left azygos, as it is often called, ascends on its own side and ends in the 
place of the left superior intercostal vein in the left vena innominata, as if by per- 
sistent connection of the left cardinal vein, with the short part of the left primitive 
jugular below the cross branch in the neck ||. 
* 1. Winslow (Exposition Anatomique, &c. t. iii. pp. 119 and 157). This example, which is clearly de- 
scribed, seems to have been overlooked. 
2. Abernetht (Philosophical Transactions, 1793, p. 69). The preparation is figured in Prof. Quain’s Ana- 
tomy of the Arteries, pi. 5. fig. 5. The aorta arches over the right bronchus as well as the vena azygos. 
3. WiSTAR (A System of Anatomy, &c. Philadelphia, 1811-14, vol. ii. p. 320). This was originally re- 
garded as an example of absence of the azygos vein, the enlarged vessel being considered as the inferior cava, 
rising higher up than usual, and ending in the vena cava superior. It is so quoted by Gurlt (^ut infra'). The 
specimen was found in 1813, and afterwards given by Wistar to Dr. Horner, by whom it has been correctly 
described and explained in the Journal of the Academy of Natural Sciences of Philadelphia, 1818, vol. i. part ii. 
p. 407 (with a plate). Otto (Lehrbuch der Anat. Patholog. p. 348, note 30) has been thus led to reckon it 
as two separate cases. 
4. Jeffray. This preparation, mentioned by Otto (op. cit. p. 348) as having been seen by him in the col- 
lection of Prof. Jeffray, is, as I am informed by Prof. Allen Thomson, now in the Museum at Glasgow. 
5. Otto himself (foe. cit. and seltene Beobacht. p. 67) met with an instance, which was afterwards fully 
described and represented by Gurlt (De Venar. Deformitatibus, &c., 1819, p. 20). 
б. Weber (Rust’s Magaz. &c. vol. xiv. p. 536). 
t Haller (op. cit. t. iii. p. 107), Winslow (op. cit. p. 121), Sandifort, three cases (Observ. Anat. Path, 
lib. ii. c. vii. p. 126, and lib. iv. p. 12). 
I Blasius (Observat. Anatom, p. 116; also Observ. Medic, p. 53. tab. 7. fig. ii. 1711). Sandifort (op. 
cit. lib. iv. p. 98). 
§ Sylvius, Jacobus (Opera Medica, Geneva, 1635, p. 144). In the body of Antonius Massa, Chirurgus, 
tw'o azygos veins were found, “ unam ab aure dextra, alteram inferiorem a cava cordi adaperta.” It is as- 
sumed by Eustachius (Opuscula, &c. p. 274) that this was an example of double azygos, one left and the 
other right, but the brevity and obscurity of the original account render it impossible to decide on its true 
nature. 
II Most of the cases recorded as examples of “ double vena azygos ” are of this kind. See Eustachius 
(Opuscula Anat. p. 274; and Explicat. Tab. Anat. by Albinus, tab. 4. figs. i. ii. hi.). Lancisi (De Vena 
sine pari, in Morgagni’s Advers. Anat. V. pp. 82, 87, 94). Winslow (Expos. Anatom. T. III. p. 121). 
