Functional morphology of the jaw adductor muscles in the Canidae.

Cranial form is closely allied to diet and feeding behavior in the Canidae, with the force and velocity of jaw-closing depending on the bony morphology of the skull and mandible, and the mass, architecture, and siting of the jaw adductor muscles. Previously, little has been reported on the details of the form and function of canid jaw adductor muscles, with earlier studies basing functional hypotheses on data derived from dry skull specimens. Here we use empirically derived muscle data from fresh-frozen specimens to explore the architecture of the muscles, and to inform finite element analyses models that predict bite force and strain energy in 12 species of wild canid. The inclusion of muscle architectural detail is shown to influence masticatory muscle force production capability calculations, indicating that muscles with longer fascicles were disadvantaged compared to muscles with shorter fascicles. No clear patterns of allometry were detected. Dietary groups were differentiated by temporalis fascicle angles, which, when allied with the differentiation of rostral length reported in previous studies, may further contribute to specializations of fast jaw-closing or forceful jaw-closing species. The most biomechanically demanding masticatory function is canine biting, and the highest strain energy values were reported in this loading condition, particularly in the zygomatic arches and caudal rostrum. Specific head shapes may be constrained by size, with scaled strain energy models predicting that some bony morphologies may only be viable in species with small body masses.

Peer-assisted learning - an antidote for spoonfeeding? Reflections on peer-assisted learning activites in a veterinary curriculum.

This article was migrated. The article was marked as recommended. Peer-assisted learning (PAL) is a potentially valuable teaching tool for students on veterinary and medical curricula, helping them to develop crucial learning, teaching and meta-adaptive skills ( Lizzio & Wilson, 2004) which will serve them during their undergraduate studies and throughout their future careers. This reflective article describes experiences of PAL activities on a UK veterinary degree course, and discusses potential reasons for success and failure of such activities. Advice is given for anyone planning to implement, or reviewing their own experiences of PAL.

Scaling and Accommodation of Jaw Adductor Muscles in Canidae.

The masticatory apparatus amongst closely related carnivoran species raises intriguing questions about the interplay between allometry, function, and phylogeny in defining interspecific variations of cranial morphology. Here we describe the gross structure of the jaw adductor muscles of several species of canid, and then examine how the muscles are scaled across the range of body sizes, phylogenies, and trophic groups. We also consider how the muscles are accommodated on the skull, and how this is influenced by differences of endocranial size. Data were collected for a suite of morphological metrics, including body mass, endocranial volume, and muscle masses and we used geometric morphometric shape analysis to reveal associated form changes. We find that all jaw adductor muscles scale isometrically against body mass, regardless of phylogeny or trophic group, but that endocranial volume scales with negative allometry against body mass. These findings suggest that head shape is partly influenced by the need to house isometrically scaling muscles on a neurocranium scaling with negative allometry. Principal component analysis suggests that skull shape changes, such as the relatively wide zygomatic arches and large sagittal crests seen in species with higher body masses, allow the skull to accommodate a relative enlargement of the jaw adductors compared with the endocranium. Anat Rec, 299:951-966, 2016. © 2016 The Authors The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology Published by Wiley Periodicals, Inc.

Effects of body position, imaging plane, and observer on computed tomographic measurements of the lumbosacral intervertebral foraminal area in dogs.

OBJECTIVE: To evaluate effects of imaging plane, flexion and extension, patient weight, and observer on computed tomographic (CT) image measurements of the area of the lumbosacral (L7-S1) intervertebral foramen (LSIF) in dogs. SAMPLE: 12 dog cadavers (2 were excluded because of foraminal stenosis). PROCEDURES: In each cadaver, sagittal, sagittal oblique, transverse oblique, and double oblique CT images were obtained at 3 zones (entrance, middle, and exit zones) of the region of the lateral lumbar spinal canal that comprises the LSIF while the lumbosacral junction (LSJ) was positioned in flexion or extension. Barium-impregnated polymethylmethacrylate was used to fill the intervertebral foramina to aid boundary detection. Measurements of interest were obtained. RESULTS: Among the dog cadavers, there was large variability in LSIF cross-sectional areas (range, 0.12 to 0.44 cm2; SD, 0.1 cm2) and in foraminal angles required to obtain a double oblique plane in LSJ extension (SD, 8 ° to 9 °). For LSIF area measurements in standard sagittal CT images, interobserver variability was 23% to 44% and intraobserver variability was 4% to 5%. Sagittal oblique images obtained during LSJ extension yielded smaller mean LSIF areas (0.30 cm2), compared with findings in sagittal images (0.37 to 0.52 cm2). The exit and middle zone areas were smaller than the entrance zone area in sagittal images obtained during LSJ extension. CONCLUSIONS AND CLINICAL RELEVANCE: Repeated measurements of the LSIF area in images obtained during LSJ extension may be unreliable as a result of interobserver variability and the effects of dog positioning and CT slice orientation.