448 
DR. PETTIGREW ON THE ARRANGEMENT OE THE FIBRES 
when explaining the construction of the right ventricle of the mammal, to discuss at 
length the peculiar fleshy valve which in the bird occupies the right auriculo-ventri- 
cular orifice. This valve constitutes, I may remark, the distinguishing feature between 
the ventricles of the bird and mammal. 
* VENTRICLES OE THE MAMMAL. 
The ventricles in the mammal are subject to considerable variation as regards shape. 
In the porpoise they have their dorsal or posterior surface flattened, and their anterior 
surface very slightly rounded, as in the higher reptiles. 
In the mysticetus the ventricles are compressed laterally, and so resemble those of 
the higher fishes. In the dugong and rhytina, they are characterized by having two very 
distinct and widely separated apices, as shown in Plate XIV. fig. 42. 
The general appearance presented by the ventricles of the mammal is familiar to all, 
it being that of an irregular cone slightly twisted upon itself. The posterior surface of 
the cone is flattened, as in the ventricle of the fish and reptile, and on account of the 
obliquity of the base is shorter than the anterior surface. The anterior surface, which 
is divided into two by an oblique sulcus or furrow, is, on the contrary, rounded and 
prominent, and presents a characteristic convex outline. Two margins or borders are 
usually described — a right inferior or acute margin (margo acutus), and a left superior 
or obtuse one (margo obtusus). As, however, these margins vary somewhat in different 
hearts, no general description concerning them can be strictly applicable. In the hearts 
of the ass, American elk, and deer tribe generally, the ventricles are rounded and taper 
towards the apex, so that the right margin appears almost as obtuse as the left ; while 
in those of the armadillo and carnivora, the ventricles, which are not taper but purse- 
shaped, have likewise the right side very obtuse*. The idea therefore of an acute 
margin ought perhaps to be confined to the right side of the human heart and a few 
others, such as the heart of the seal and hog, both of which bear a considerable resem- 
blance to that of man. 
The base of the cone formed by the ventricles of the mammal, as is well known, is 
perforated by four openings. These openings are surrounded by fibrous rings, and con- 
duct to conical-shaped spiral cavities f, which vary somewhat in size according as the 
carnete columnse are absent J or present, and the musculi papillares feebly or fully 
developed. 
Considered as a muscle, the heart, and especially the ventricular portion of it, is 
peculiar. Being in the strictest acceptation of the term an involuntary muscle, its 
fibres nevertheless possess the dark colour, and transverse markings, which are charac- 
* Between these extremes in shape may be ranted the ventricles of the camel, horse, ox, giraffe, calf, hare, 
rabbit, &e. 
t See photograph of a wax cast of the interior of the ventricles of a deer’s heart, Plate XII. figs. 16 & 17, 
and transverse sections, Plate XY. figs. 49 to 53 inclusive. 
+ The ventricles of the American elk are devoid of carnese columnas, as are likewise those of the red deer 
(Plate XY. fig. 48). 
