182 MR. F. E. BEDDARB ON THE [Feb. 19, 



for he wi-ote, " L'insertion de Yazygos, Texistence d'une azygos du 

 cote gaxiclie sont assez variables ; mais on salt que les memes 

 circonstances varient dans I'homme. Elles ne ineritent pas con- 

 sequeniment de nous arreter." Milne-Edwards*, on the other 

 hand, and rightly, treats these veins as of importance, and tabu- 

 lated the main variations. These statements really express the 

 main facts as we know them today. With reference to the 

 Marsupials, indeed, the asseition of Milne-Edwards seems to me 

 to be nearer to the truth than some generalisations made more 

 recently. This group is placed by Milne-Edwards under the 

 heading " Les deux veines azj^gos egalement developpees." 

 Although I shall show reasons for slightly criticising this state- 

 ment, it is not greatly exaggerated. On the other hand, in 

 denying the existence of a right azygos (" Point de veine azygos 

 a droite ") in the Sheep, Ox, Goat, Ohevrotain, Pig, and Tapir he is, 

 in my opinion, not by any means so accurate. With regard to 

 the Tapir there is some error in Milne-Edwards's statement ; for 

 he also places that animal under the heading of those animals 

 which only possess a right azygos. Sir Richard Owen's classical 

 text-book, published ten years later than the volume of Milne- 

 Edwards's great work, adds but little to the record of facts con- 

 cerning the a,zygos veins. There are, however, numerous scattered 

 references to the condition of these veins in various mammals by 

 Owen and others, to some of which I am able to refer in the 

 course of the following pages. 



Many of these papers a,re quoted by Hochstetterf in his 

 memoir dealing with the development of the Azygos (and other 

 veins) in the Mammalia. A large number, however, relate to 

 tlie condition of the azygos in man, and I do not attempt here to 

 follow up that very large subject. I limit myself to such other 

 mammals as I have been able to dissect, in many of which the 

 azygos has not been described. The classificatory importance of 

 the azygos has been recognised by Dr. Max Weber +, and there is 

 no doubt that its conditions are often distinctive of genera or of 

 whole orders of mammals. I propose, however, to deal with this 

 matter after exposing the facts which T have gathered together 

 by degrees during several years of intermittent work upon the 

 subject, which is a larger collection of facts concerning this vein 

 than has previously been brought together. 



Opinion with regard to the morphological nature of the azygos 

 veins has lately undergone some change. Until lately the pre- 

 valent view was that one or both of the postcardinals persisted as 

 the Azygos, the Hemiazygos, or both. This view is embodied in 

 diagrams in many text-books. 



Of recent writers Messrs. Parker and Tozier § appear to hold 



* Anat. et Phys. Comp. vol. iii. (Paris, 1858) pp. 595-598. 



f Movph. .Jalirb. xx. 1893, p. 642 &c. Milne-Edwards's resume is largely based 

 upon the observations of Bardeleben (Arch. f. Anat. u. Phys. 1848) and Marshall 

 {" Development of great Anterior Veins &c.," Phil. Trans. 1850). 



J Die Saugetiere, .Jena, 1904. 



§ " Postcai'diiial Veins in Swine," Bull. Mus. Comp. Zool. vol. xxxi. 1898, p. 133. 



