IN THE VENTRICLES OF THE VERTEBRATE HEART. 
479 
oblique spiral direction from behind forwards and from right to left upwards; and 
are aggregated into well-marked fascicular bundles which are continuous anteriorly 
(Plate XIV. fig. 36, o) and for the most part posteriorly with fibres having a like direc- 
tion on the right third of the septum (p'q'). They are continuous also with the fibres 
of the third external layer at the base. As the common fibres do not extend to, or im- 
plicate the internal layers, the fibres of the right third of the septum readily become 
continuous with internal fibres on the posterior wall having a corresponding direction 
(Plate XIV. fig. 32, p q). The fibres of the fifth layer (Plate XIV. fig. 32) split up or 
bifurcate at a point corresponding with the fleshy pons, into the formation of which they 
enter, the one half bending over in a direction from without inwards (to) to become 
continuous with fibres from the septum having a similar direction — the other half curving 
round the infundibuliform portion of the right ventricle anteriorly (p') to dip in at the 
track for the anterior coronary artery (Plate XIII. fig. 26, o ), from which they emerge 
with the septal fibres referred to. The fibres of the fifth layer seldom make more than 
one turn of a spiral, many of them, from terminating at the root of the aorta and septum 
anteriorly, making less. 
Sixth layer of right ventricle (Mammal). The fibres of the sixth layer of the right 
ventricle (Plate XIV. fig. 33) agree in their more important features with the fibres of 
the fifth layer ; i. e. they proceed in a spiral direction from right to left, or from behind 
forwards and from below upwards (pp 1 , q #'), the fibres bifurcating (to (f) to assist in form- 
ing the fleshy pons (to) and the infundibulum (q'). The fibres of the sixth layer agree 
with those of the fifth in being continuous anteriorly (Plate XIV. * fig. 37, w) and 
posteriorly (Plate XIV. fig. 33, p q) with fibres having a similar direction on the septum 
(Plate XIV. fig. 37, p'q'), and with corresponding external fibres (the fibres of the second 
layer) at the base (Plate XIV. fig. 31 ,ff, dd'). The fibres of the sixth layer differ from 
those of the fifth in pursuing a slightly more vertical direction, and in not being quite 
so fascicular. They form the homologues of the fibres of the second layer. 
Seventh or last internal layer of right ventricle (Mammal). The fibres of the seventh 
or last internal layer of the right ventricle are those principally engaged in the forma- 
tion of the carnese columnse and musculi papillares of the right ventricle, and have been 
already described. 
The points established with reference to the right ventricle are these : — 
1st. Many of the fibres entering into the formation of the right ventricular wall pro- 
ceed from the left auriculo-ventricular opening, so that the right ventricle is to a certain 
extent dependent for its existence on the left. 
2ndly. The external fibres of the right ventricle, with the exception of a broad band 
at the base, limited to the first two external layers, dip in at the track for the anterior 
coronary artery, to appear on the septum. 
3rdly. Many of the fibres, especially of the deeper layers, are continuous anteriorly 
* In Plate XIII. fig. 29, the fibres in question ( p q) are seen dipping in at the anterior coronary track 
(oo'). 
3 s 2 
