DR. J. MURIE ON THE ORGANIZATION OF THE CAAING WHALE. 267 
other words, the valve consisted of two segments, the delicate free margins of the 
segments being supplied with numerous fine chorde tendinee attached to the rudi- 
mentary musculi papillares of the right ventricle. From this it follows that the 
supplementary mitral valve within the septal segment of the tricuspid (this valve 
within a valve) appears to be acted upon by the musculi papillares and by the blood, 
precisely in the same manner as the mitral and tricuspid valves themselves; 7. é. it is 
opened during the diastole of the heart, and closed during its systole. 
By reference to figures 52 & 53 a better conception of the position of the perforation 
and its relation to the tricuspid will be gathered than by entering into minutiz verbally. 
I may remark, however, that this ancillary valve, whatever its homological significance, 
appears to me to be to the valvular system of the heart, what the rete mirabile is to 
the vascular system generally. One may regard it as a tendency in nature to repeat 
herself, a something superadded without apparently any special end to be served. It 
may be imagined to weaken rather than strengthen the action of the tricuspid; on the 
other hand, it may be a kind of safety-valve’. From its anatomical structure, its 
physiological influence can only be conjectured. ‘The rarity of such an instance shows 
that it is not a necessity to Cetacean circulation. 
I a Nr 
The arch and great arteries of the Pilot Whale, after Turner, from the Journ. of Anat. ii. p. 67. 
A, aorta; P, pulmonary artery; D, ductus arteriosus; @, carotis cerebralis, the diminution in calibre of this artery in the course 
of its ascent is not sufficiently represented in the figure; 4, carotis facialis; c, subclavia; d, cervico-occipalis ; e, thoracica 
posterior dextra; f, transyersalis colli; g, mammaria interna; h, thoracica posterior sinistra. 
* See a paper by T. King “On the Safety-valve Functions in the Right Ventricle of the Heart,” Guy’s Hosp. 
Reports, vol. ii. : 
VoL. Vul.—ParT Iv. February, 1873. 2Q 
