474 
DR PETTIGREW ON THE ARRANGEMENT OE THE EIBBES 
separates the right auriculo-ventricular opening (l) from that of the pulmonary artery (k). 
This fibrous archway has been appropriately denominated the fleshy pons, and is more or 
less spindle-shaped, from the fact of its forming the boundary between the auriculo- 
ventricular and pulmonic orifices, the former of which is oval, the latter circular. It 
varies in size according to the dimensions of the heart. In the sheep, calf (Plate XIV. 
fig. 43, m ), hog, leopard, deer, and seal it is usually about half an inch in breadth at 
its narrowest portion, and rather less than a quarter of an inch in thickness ; while in 
the giraffe, camel, and horse it increases to twice these dimensions. 
Another peculiarity in the right ventricle of the mammal, to which a passing allusion 
is due, appears in the form of a conical-shaped projection (Plate XIV. fig. 37, w), the 
so-called infundibulum (Cruveilhier), or conus arteriosus (Wolff*), situated at the 
upper and anterior portion (p) of the ventricle. This projection, which communicates 
above or at its summit with the pulmonary artery (#), has the effect of lengthening the 
right ventricle towards the base to the extent of half an inch or so in moderate-sized 
hearts, and in this way makes up the deficiency of the right ventricle towards the apex. 
The vertical measurement of the right and left ventricles is consequently nearly equal. 
The conus arteriosus is composed externally f of fibres which arise more immediately 
from the fibrous ring surrounding the orifice of the pulmonary artery (Plate XV. 
fig. 46, k ) — these fibres having a plicated or tortuous arrangement (c), similar to that 
which occurs in the superficial layer of the ventricle of the fish and reptile. As, how- 
ever, the fibres alluded to are separable into layers (Plate XIV. figs. 30 & 31, k), and 
are continuous with the fibres of the external layers of the right ventricle generally, with 
which they correspond in direction ( fd ), they are not entitled to a separate description. 
The more internal portions of the conus arteriosus are composed of the internal layers 
of the right ventricle. An additional peculiarity in the right ventricle of the mammal 
consists in the existence, in a large number of quadrupeds, of a curiously shaped bone 
(Plate XIV. figs. 30 & 31, c) which is imbedded in the right side (a) of the fibro-cartila- 
ginous ring surrounding the aortic orifice. The bone in question, on account of its being 
more fully developed in some instances than in others J, varies considerably as regards 
* “ This author drew a distinction between the conus arteriosus and the infundibulum, applying the former 
epithet to that portion of the ventricle from which the pulmonary artery springs, and which is prolonged up- 
wards above the level of the rest of the ventricle. In the term infundibulum he included a larger portion of 
the ventricle, apparently that portion placed above a line drawn from the upper and right margin of the ven- 
tricle obliquely downwards to the anterior fissure. As the upper part of the right ventricle becomes gradually 
narrower, he supposed that it increases the velocity and impetus of the blood as it is drawn from the ventricle.” 
(Acta Acad. Imper. Petropol. pro anno 1780, tom. v., vi. p. 209, 1784.) 
f The arrangement of the fibres entering into the composition of the conus arteriosus interiorly is described 
at p. 479. 
t Blttmemach (Comparative Anatomy, translated by Mr. Lawrence, p. 138) speaks of two bones as existing 
in the heart of the stag and the larger adult bisulca. According to Mr. W. S. Savory, two principal bones (a 
larger and a smaller), together with several irregular fragments, are found in the hearts of the larger ruminants. 
(Observations on the Structure and Connexions of the Yalves of the Human Heart, 1851.) The author of the 
present paper has occasionally seen the fragments alluded to by Mr. Savory. 
