of Edinburgh^ Session 1863-64. 
193 
1. Od the Anatomy and Physiology of the Mitral, Tricus- 
pid, and Semilunar Yalves in Mammals, Birds, Keptiles, 
and Fishes. By James B. Pettigrew, M.D., Edinburgh ; 
Assistant in the Museum of the Eoyal College of Sur- 
geons of England. Communicated by Wm. Turner, M.B. 
The writer begins his communication by giving a brief de- 
scription of the structures in which valves are found, and takes 
occasion to comment on the nature and properties of the veins and 
arteries, and on the arrangement of the muscular fibres in the 
ventricles, as these necessarily influence, to a greater or less 
extent, the action of the valves. He also adverts at some length 
to the shape of the venous, arterial, and auriculo-ventricular 
orifices, and to the fibro-cartilaginous rings by which the latter are 
surrounded ; as well as to the dilatations or sinuses which are found 
behind or to the outside of the segments constituting the semilunar 
valves in the veins and arteries, and to the shape of the ventricular 
cavities, which, as he points out, bear an important relation to the 
valves, inasmuch as they determine the direction in which the 
blood acts upon them ; precise information on these points being, 
according to the author, indispensable to a just appreciation of the 
subject under investigation. 
The object of the Memoir is to prove that in the valves, as in 
other structures where modifications occur, we rise from the simple 
to the more complex ; in other words, that the valves form a 
differentiated and gradually ascending series. 
In the veins, e. g., the valve consists of a doubling of the delicate 
membrane lining the vessel, containing some fibro-cellular and 
elastic tissue, the distribution of which in the horse can be readily 
made out. The segments of the valve are semi-transparent, and, as 
a rule, semilunar in shape. They are further placed obliquely, one 
only being present in the smallest veins, two in the middle-sized 
ones, and three in the largest. Behind each segment there is a 
dilatation or bulging of the vessel, which projects nearly as far in 
an outward direction as the segment extends inwardly, and gives 
to the latter the requisite degree of curvature. As the dilatation 
referred to enables the lining membrane which forms the segments 
