A salamander that chews using complex, three-dimensional mandible movements.

Most non-mammal tetrapods have a hinge-like jaw operation restricted to vertical opening and closing movements. Many mammal jaw joints, by contrast, operate in more complex, three-dimensional (3D) ways, involving not only vertical but also propalinal (rostro-caudal) and transverse (lateral) movements. Data on intraoral food processing in lissamphibians and sauropsids has prompted a generally accepted view that these groups mostly swallow food unreduced, and that in those cases where lissamphibians and sauropsids chew, they mostly use simple vertical jaw movements for food processing. The exception to this generally accepted view is the occurrence of some propalinal chewing in sauropsids. We combined 3D kinematics and morphological analyses from biplanar high-speed video fluoroscopy and micro-computed tomography to determine how the paedomorphic salamander Siren intermedia treats captured food. We discovered not only that S. intermedia uses intraoral food processing but also that the elaborated morphology of its jaw joint facilitates mandibular motions in all three planes, resulting in complex 3D chewing. Thus, our data challenge the commonly held view that complex 3D chewing movements are exclusive to mammals, by suggesting that such mechanisms might have evolved early in the tetrapod evolution.

The importance of the evolutionary heritage of locomotion on flat ground in small mammals for the development of arboreality.

The earliest representatives of the mammalian stem line were small. Recent small mammals preserving their morphology possess rather similar kinematic and dynamic locomotor patterns, even if they are not closely related. For a small animal, the mechanics of locomotion on a large branch is comparable to locomotion on flat ground. Combining these informations, it seems sensible to start a discussion on the origins of arboreality with a detailed analysis of the locomotion of small mammals on flat ground. For this purpose, the kinematics of twelve species of mammals were observed using cineradiography, a "general limb" of small mammals was derived as a principle, and its interactions with the trunk were analyzed. These data form the basis for a theoretical upscaling of the motion patterns in arboreal animals, revealing that the transfer of torques between animal and branch becomes unavoidable, thus making the use of prehensile hands advantageous, which by their tendency of distal concentration of muscle masses force the need to change the basic kinematic patterns.

Arboreal locomotion in small new-world monkeys.

The postural and locomotor activity and its relation to substrates was observed in 3 Saguinus oedipus, and 3 Saimiri sciureus for comparison, during a period of 10 h for each individual. The animals moved freely in cages of 3.40 m x 3.40 m x 2.40 m (height) on rather diverse substrates. Observations were made according to the focal-animal-method, with combined instantaneous and continuous sampling. They were protocoled in schematic form and video-recorded. In addition, 3 further Saguinus oedipus were subjected to an X-ray cinematographic study on a modified treadmill to unveil metric parameters of the locomotor pattern preferred on slender and compliant ("arboreal") substrates, the walk. Independent from the substrates, the postures of the two species differed in details, as do the preferred substrates. Horizontal, comfortable substrates are favored most. Walking ranked top in frequency, followed by jumping and galloping (in a strict sense). All other locomotor modes described for primates played a minor role or lacked entirely, like the trot. Average distance of leaps was only 0.60 m, landings were mainly on the same level as take-offs. In Saguinus, the movements of both limbs, including the shoulder blade, followed the pattern common to small mammals in general: At the end of the stance phase, humerus and tibia are nearly parallel to the substrate, while just before touchdown ulna and femur are in this position. The walk in both species was surprisingly fast (1 m/s), reaching the speed of much larger cursorial animals, like humans.

Shoulder movements during quadrupedal locomotion in arboreal primates.

The kinematics of scapula and shoulder joint movements were analyzed in three species of arboreal quadrupedal primates using cineradiography. Our findings indicate that scapular movement is highly important for forelimb movement in primates with this ancestral mode of locomotion. Retroversion of the scapula (syn. caudal rotation or extension) during the stance phase contributes more than 40% to the stride length of the forelimb. Lateral forelimb excursions, a general feature for arboreal primates, are based on complex three-dimensional scapular movements guided by the clavicle. Humeral abduction is achieved by scapular abduction and transversal rotation of the scapula about its longitudinal axis, and is therefore strikingly different from humeral abduction in humans. At the same time, the movements of the shoulder joint are limited to flexion and extension only.

Evaluation of a standardised questionnaire for the detection of dysphagia in 69 dogs.

The diagnosis of dysphagia in the dog requires an evaluation of a variety of signs that can be caused not only by a 'swallowing disorder' but also by several other pathological conditions. Most owners mention coughing, vomiting, regurgitation and nasal discharge, and the clinician must decide whether these signs are related to dysphagia. In this study a standardised questionnaire for the diagnosis and localisation of dysphagia was evaluated for its accuracy by comparing the results with contrast videofluorography as the definitive standard. The purpose of the study was to optimise the selection of dogs for more expensive diagnostic procedures such as videofluorography and electromyography. In a group of 69 dogs with 'swallowing problems' the questionnaire had a sensitivity of 0.97 and a positive predictive value of 0.94 for dysphagia in general. The questionnaire was also useful for the exclusion of oral phase dysphagia, with a specificity of 0.70 and a negative predictive value of 0.97. Most dogs with pharyngeal phase dysphagia could be detected by using the questionnaire (sensitivity 0.91). The questionnaire was not of specific value for the detection or exclusion of oesophageal phase dysphagia, for which it had a sensitivity of 0.69, a specificity of 0.57 and predictive values for positive and negative tests of 0.79 and 0.44, respectively.

Muscle force recruitment and biomechanical modeling: an analysis of masseter muscle function during mastication in Macaca fascicularis.

The main purpose of this study is to test the hypothesis that as subjects chew with increasing levels of force, the ratio of the working- to balancing-side jaw-muscle force (W/B) decreases and begins to approach 1.0. We did this by analyzing relative masseter force in Macaca fascicularis using both strain gage and surface electromyographic (EMG) techniques. In addition, we also analyzed: 1) the relationship between jaw position using cineradiographic techniques and relative masseter force, 2) the timing differences between relative masseter force from the working and balancing sides, and 3) the loading and unloading characteristics of the masseter muscle. Our findings indicate that when macaques increase the amount of overall masticatory force during chewing, the W/B ratio for masseter force frequently (but not always) decreases and begins to approach 1.0. Therefore, our working hypothesis is not completely supported because the W/B ratio does not decrease with increasing levels of force in all subjects. The data also demonstrate timing differences in masseter force. During apple-skin mastication, the average peak masseter force on the working side occurs immediately at or slightly after the initial occurrence of maximum intercuspation, whereas the average peak masseter force on the balancing side occurs well before maximum intercuspation. On average, we found that peak force from the balancing-side masseter precedes the working-side masseter by about 26 msec. The greater the asynchrony between working- and balancing-side masseter force, the greater the difference in the relative magnitude of these forces. For example, in the subject with the greatest asynchrony, the balancing-side masseter had already fallen to about one-half of peak force when the working-side masseter reached peak force. Our data also indicate that the loading and unloading characteristics of the masseter differ between the working and balancing sides. Loading (from 50 to 100% of peak force) and unloading (from 100 to 50% of peak force) for the balancing-side masseter tends to be rather symmetrical. In contrast, the working-side masseter takes much longer to load from 50 to 100% of peak force than it does to unload from 100 to 50% of peak force. Finally, it takes on average about 35 msec for the working-side zygoma and 42 msec for the balancing-side zygoma to unload from 100 to 50% of peak force during apple-skin mastication, indicating that the unloading characteristics of the macaque masseter during mastication closely approximates its relaxation characteristics (as determined by muscle stimulation).

Radiologic observations of gastric mixing and emptying of food in growing pigs.

The stomachs of 10 Large White x Landrace pigs were examined radiographically from weaning (at 26 to 28 days of age) until 6 or 16 weeks of age. Conventional radiographs were taken and observations were made with a television chain and 35-mm cinecamera linked to an image intensifier. Before radiography, each animal was fed its normal diet that contained a barium sulfate suspension and/or radio-opaque pellets. The basic pattern of motility in the major chamber of the pig's stomach was similar to that described in animals with a simple stomach. Type II peristaltic waves were clearly identified as indentations of the body of the stomach that moved towards the pyloric antrum, which became circular as it filled with digesta. A terminal antral contraction then occurred, the antrum decreased in diameter, and the ingesta and barium sulfate either entered the duodenum or were returned to the body of the stomach. Liquids and finely ground food left the stomach more rapidly than did the radio-opaque pellets that were retained for up to 44 hours. The radio-opaque pellets demonstrated the movement of ingesta within the gastric lumen and showed that ingesta was retropulsed into the body of the stomach by the terminal antral contraction. In 4 pigs, barium and ingesta were present in the 2nd chamber of the stomach, the gastric diverticulum. In 1 pig, a movement of the diverticulum was observed on a single occasion.