482 
DE. PETTIGEEW ON THE AEEANGEMENT OF THE FIBEES 
3rdly. The musculi papillares (xy) of the left ventricle (b) are very prominent, the 
left ventricular cavity ( b ) from this circumstance being more triangular in shape than in 
the second section (Plate XV. fig. 50). 
4thly. The right ventricular cavity (l), from its proximity to the right apex, is more- 
over greatly reduced in size. 
In a transverse section three and a half inches from the base, and fully half an inch 
from the left apex (Plate XV. fig. 52) — the right apex is now removed — the subjoined 
results are obtained : — 
1st. The preponderance of the internal ( d d') over the external (c c') fibres is still more 
marked, illustrating the necessity for the internal fibres overlapping and crowding on 
their appearance in the interior, more especially at the apex, where the cavity is greatly 
reduced. 
2ndly. The circular nature of the more central fibres (e e') is still better defined, many 
of the external fibres at this point reversing their direction to become internal. 
3rdly. The musculi papillares are very prominent, the external fibres which have just 
entered the interior being seen to curve into them ( xy ). 
4thly. The left ventricular cavity (£), from the comparatively large dimensions of the 
musculi papillares, is greatly diminished *; and the form of the left ventricular cavity is 
more or less bayonet-shaped. 
In a transverse section a quarter of an inch from the extremity of the left apex 
(Plate XV. fig. 53), the peculiarities of the preceding section (fig. 52) are found exagge- 
rated. Thus the quantity of the internal as compared with the external fibres is in- 
creased — the more central fibres (e <?'), from the great number of external ones which at 
the apex change their direction to become internal, curving round in a regular whorl, 
many of them entering directly into the composition of the musculi papillares (xy); 
the left ventricular cavity is now all but closed. 
Casts of the interior of the right and left ventricles (Mammal). 
When casts of the interior of the ventricles are taken, the left ventricular cavity 
(Plate XII. fig. 17), as has been stated, yields a highly symmetrical conical screw whose 
spiral runs from left to right downwards, the right ventricular cavity (Plate XII. fig. 16) 
yielding a more unsymmetrical one — unsymmetrical in this sense, that it is flattened out 
and applied to or round the left. The amount of spiral made by the left ventricular 
cavity is rather over a turn and a half ; that made by the right ventricular cavity rather 
under a turn. 
* In this and the following section, the cavity of the left ventricle, towards the apex, would he at once obli- 
terated by a slight approximation of the musculi papillares — this approximation ef the papillary muscles being 
effected by the contraction of the spiral nearly circular fibres which constitute the apex. By this arrangement, 
the apex, which is the weak part of the ventricle, can be readily converted into a solid muscular wall capable 
of resisting any amount of pressure. 
