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SUMMARYVascular pressure separation by virtue of a two-chambered ventricle evolved independently in mammals and birds from a reptilian ancestor with a single ventricle, and allowed for high systemic perfusion pressure while protecting the lungs from oedema. Within non-crocodilian reptiles, ventricular pressure separation has only been observed in varanid lizards and has been regarded as a unique adaptation to an active predatory life style and high metabolic rate. The systemic and pulmonary sides of the ventricle in Python molurusare well separated by the muscular ridge, and a previous study using in situ perfusion of the heart revealed a remarkable flow separation and showed that the systemic side can sustain higher output pressures than the pulmonary side. Here we extend these observations by showing that systemic blood pressure Psys exceeded pulmonary pressure Ppul almost seven times (75.7±4.2 versus11.6±1.1 cm H2O). The large pressure difference between the systemic and pulmonary circulation persisted when Psys was altered by infusion of sodium nitroprusside or phenylephrine. Intraventricular pressures, measured in anaesthetised snakes, showed an overlap in the pressure profile between the pulmonary side of the ventricle (cavum pulmonale) and the pulmonary artery, while the higher pressure in the systemic side of the ventricle (cavum arteriosum) overlapped with the pressure in the right aortic arch. This verifies that the pressure differences originate within the ventricle, indicating that the large muscular ridge separates the ventricle during cardiac contraction.

Twelve Dutch vowels, each pronounced by 50 male speakers, were analyzed in 18 filter bands comparable in bandwidth with the cat's critical band. By considering the sound levels (in decibels) in these filter bands as dimensions, with a principal-component analysis the 18 dimensions per sound were reduced to four factors which together explain 75% of the total variance. The configuration of the average vowels in the factor space appeared to be highly correlated with their configuration in the Fx-F• formant plane. After matching to maximal congruence, correlation coefficients along corresponding axes were 0.997 and 0.979. Machine vowel identification, based upon the position of the individual vowels in the four-dimensional factor space, resulted (after three pairs of related vowels were grouped together) in 98% correct identifications if correction was applied for personal timbre of the speakers' voices. Ten listeners, to whom the 600 vowels were presented as 100-msec segments, gave 86% correct responses in identifying the intended vowels. The confusions between the vowel types were basis for a multidimensional scaling (Kruskal) to construct a perceptual configuration of the vowels. In four dimensions the solution showed 2.3% stress. Perceptual configuration and factor configuration, maximally matched, had correlation coefficients along corresponding axes of 0.997, 0.995, 0.907, and 0.794, respectively.

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Aspiration breathing is the dominant mechanism of lung inflation among extant amniotes. However, aspiration has two fundamental problems associated with it: paradoxical visceral translation and partial lung collapse. These can constrain the inspiratory tidal volume, reduce the effective lung ventilation, and ultimately curtail the aerobic capacity of an animal. Separation of the pleural and peritoneal cavities by an intracoelomic septum can restrict the cranial shift of abdominal viscera and provide structural support to the caudal lung surface. A muscular septum, such as the diaphragm of mammals or the diaphragmaticus of crocodilians, can exert active control over visceral translation and the degree of lung inflation. To a lesser degree, a nonmuscular septum can also function as a passive barrier when stretched taut by rib rotation. Studies of the posthepatic septum in teiid lizards and the postpulmonary septum in varanid lizards underscore the importance of nonmuscular septa in aspiration. These septa provide plausible functional models that help us infer the evolution of mammalian and avian lung ventilatory systems, respectively.