THE HEART. 327 



then proceeded to give an account of the results of his own investiga- 

 tions, -which had been conducted on the hearts of the sheep, calf, deer, 

 ox, horse, &c., all of which, he observed, bear a perfect resemblance to 

 the human heart.* In order, as much as possible, to evercome the 

 difficulties of the subject, he availed himself of drawings, explanatory 

 diagrams, and models illustrating the course and relation of the fibres, 

 To these last, however, he observed, he attached no special importance, 

 further than that they were useful vehicles of communication ; and it 

 was to the dissections themselves, some of which were before the 

 Society, that he looked for a corroboration of the statements he ad- 

 vanced. 



" Commencing with the left ventricle, which he believes to be the 

 typical one, the Lecturer stated that, by exercising a little care, he 

 had been enabled to unwind, as it were, its muscular substance, and 

 so to separate its walls into several layers,t each of which is charac- 

 terised by a difference in direction. Seven layers, at least, can be 

 readily shown by dissection: but he believes they are in reality nine; 

 viz., four external, the fifth or central, and four internal. He ex- 

 plained how the external fibres are continuous with the internal fibres 

 at the apex, as was known to Lower,t Gerdy, and others, and how 

 the fibres constituting the several external layers are continuous with 

 corresponding internal layers likewise at the base;[] a fact to which 

 the Lecturer drew particular attention, as being contrary to the gene- 

 rally received opinion, which is to the effect that the fibres at the 

 base are non-continuous, and arise from the auriculo-ventricular ten- 



* Dr Pettigrew's researches include also the arrangement of the fibres in 

 the ventricles of the bird, reptile, and fish. 



f Senac (Traite de la Structure du Cceur, &c., [Paris, 1749], planche 8), 

 figures four layers; and Searle (Cyc. of Anat. and Phys., art. "Heart," 

 speaks of three. 



I Tractatus de Corde, &c. London, 1669. 



Recherches, Discussions et Propositions cT Anatomic, Physiologic, &c. 

 Paris, 1836. 



|| The late Dr Duncan, jun., of Edinburgh, was aware of the fibres form- 

 ing loops at the base, but seems to have had no knowledge of the continuity 

 being occasioned by the union of corresponding external and internal layers, 

 or that these basal loops were prolongations of like loops formed by similar 

 corresponding external and internal layers at the apex a point which the 

 Lecturer believes he is the first to establish. 



