Moreover, there are propositions which Galen firmly believes, and which indeed are central to his physiological system, which he does not claim to be able to establish on the basis of epistemonic premisses; these “do not have such an evident demonstration” as the former (PHP VI.3, 373; cf. VIII.1, 486–8), yet it seems in these cases that the lower-grade demonstration is regarded as adequate. Such, in particular, are the proofs of the location of the remaining two parts of the soul, the spirited (in the heart) and the desiderative (in the liver). The proof of the location of the rational in the brain—which famously involves vivisectional experiments on animals, showing their loss of speech and mobility when the spinal cord is ligated—Galen takes to be epistemonic. The propositions that the heart is in the seat of the spirited, meanwhile, and that the liver is the seat of the desiderative, rely on premisses which are not based directly on the ousia of the subject, but rather (again using Aristotelian terminology), on its “specific properties” (sumbebēkota idiai). What this means in effect is that Galen must here rely on proofs from plausibility and analogy. For example, the proposition that the heart is the seat of the spirited part of the soul—the part involved in responses of anger and indignation—gains plausibility from the fact that one observes perturbations of the heart in certain particular excited states of mind. The proposition that the liver is the seat of the desiderative, which may be equated with the nutrititive and reproductive, is supported by the liver’s role as source of the veins; and this in turn relies for its plausibility on an analogy with plants: the bigger (trunk) is the source of the smaller (branches).