494 
DE. PETTIGREW ON THE ARRANGEMENT OE THE FIBRES 
Fig. 31. Right ventricle of the sheep’s heart. Shows the bone of the heart in situ , the 
direction of the fibres of the third external layer, &c. See page 476. 
Note . — The fourth or central layer of the right ventricle is seen at p q of 
fig. 23, Plate XIII. 
Fig. 32. Right ventricle of the sheep’s heart. Shows the direction of the fibres of the 
fifth layer of the right ventricle, fleshy pons, &c. See pages 478 & 479. 
Fig. 33. Right ventricle of the sheep’s heart. Shows the direction of the fibres of the 
sixth layer of the right ventricle. See page 47 9. 
Fig. 34. Right ventricle of the sheep’s heart, seen anteriorly and from the left side. 
Shows the first layer of the septum dissected from within, or from the left 
side, and how the fibres of the first external layer of the right ventricle bend 
or double upon themselves to become continuous with fibres having a similar 
direction on the septum. See page 468. 
Note . — The second layer of the right ventricle is omitted. (See f d' of 
fig. 22, Plate XIII.) 
Fig. 35. Right ventricle of the sheep’s heart, seen anteriorly and from the left side. 
Shows the fibres of the third layer of the septum dissected from within or 
Horn the left side, and how the fibres of the third layer of the right ven- 
tricle bend or double upon themselves, anteriorly and posteriorly, to become 
continuous with those on the septum having a similar direction. See 
page 476. 
Note . — The fourth or central layer of the right ventricle is omitted. (See 
pq of fig. 23, Plate XIII.) 
Fig. 36. Right ventricle of the sheep’s heart, seen anteriorly and from the left side. 
Shows the fibres of the septum dissected from within or from the left side, as 
in the two preceding figures, also how the fibres of the fifth layer of the right 
ventricle are continuous on the septum, anteriorly and posteriorly. See pages 
478 & 479. 
Fig. 37. Right ventricle of the sheep’s heart, seen anteriorly and from the left side. 
Shows the fibres of the septum dissected from within or from the left side, as 
in the three preceding figures, also how the fibres of the sixth layer are con- 
tinuous on the septum, anteriorly and posteriorly. See page 479. 
Note . — The seventh or last internal layer is omitted. 
Fig. 38. Bird’s-eye view of the base of the ventricles, of the swan’s heart. Shows the 
right and left auriculo-ventricular openings, with the muscular and bicuspid 
valves in situ. See pages 470, 471, & 472. 
Fig. 39. The ventricles of the heart of the swan, seen from the right side. Shows the 
right side of the septum and the posterior portion of the muscular valve in 
position ( g ), also how the fibres from the upper third of the septum and left 
ventricle posteriorly enter into the formation of the inner half of the muscu- 
lar fold. See pages 470, 471, & 472. 
