A 3D interactive model and atlas of the jaw musculature of Alligator mississippiensis.

Modern imaging and dissemination methods enable morphologists to share complex, three-dimensional (3D) data in ways not previously possible. Here we present a 3D interactive model of the jaw musculature of the American Alligator (Alligator mississippiensis). Alligator and crocodylian jaw musculature is notoriously challenging to inspect and interpret because of the derived nature of the feeding apparatus. Using Iodine-contrast enhanced microCT imaging, a segmented model of jaw muscles, trigeminal nerve, brain and skull are presented as a cross-sectional atlas and 3D, interactive pdf of the rendered model. Modern 3D dissemination methods like this 3D Alligator hold great potential for morphologists to share anatomical information to scientists, educators, and the public in an easily downloadable format.

Trigeminal nerve morphology in Alligator mississippiensis and its significance for crocodyliform facial sensation and evolution.

Modern crocodylians possess a derived sense of face touch, in which numerous trigeminal nerve-innervated dome pressure receptors speckle the face and mandible and sense mechanical stimuli. However, the morphological features of this system are not well known, and it remains unclear how the trigeminal system changes during ontogeny and how it scales with other cranial structures. Finally, when this system evolved within crocodyliforms remains a mystery. Thus, new morphological insights into the trigeminal system of extant crocodylians may offer new paleontological tools to investigate this evolutionary transformation. A cross-sectional study integrating histological, morphometric, and 3D imaging analyses was conducted to identify patterns in cranial nervous and bony structures of Alligator mississippiensis. Nine individuals from a broad size range were CT-scanned followed by histomorphometric sampling of mandibular and maxillary nerve divisions of the trigeminal nerve. Endocast volume, trigeminal fossa volume, and maxillomandibular foramen size were compared with axon counts from proximal and distal regions of the trigeminal nerves to identify scaling properties of the structures. The trigeminal fossa has a significant positive correlation with skull length and endocast volume. We also found that axon density is greater in smaller alligators and total axon count has a significant negative correlation with skull size. Six additional extant and fossil crocodyliforms were included in a supplementary scaling analysis, which found that size was not an accurate predictor of trigeminal anatomy. This suggests that phylogeny or somatosensory adaptations may be responsible for the variation in trigeminal ganglion and nerve size in crocodyliforms.

Facial phenotypes in subgroups of prepubertal boys with autism spectrum disorders are correlated with clinical phenotypes.

BACKGROUND: The brain develops in concert and in coordination with the developing facial tissues, with each influencing the development of the other and sharing genetic signaling pathways. Autism spectrum disorders (ASDs) result from alterations in the embryological brain, suggesting that the development of the faces of children with ASD may result in subtle facial differences compared to typically developing children. In this study, we tested two hypotheses. First, we asked whether children with ASD display a subtle but distinct facial phenotype compared to typically developing children. Second, we sought to determine whether there are subgroups of facial phenotypes within the population of children with ASD that denote biologically discrete subgroups. METHODS: The 3dMD cranial System was used to acquire three-dimensional stereophotogrammetric images for our study sample of 8- to 12-year-old boys diagnosed with essential ASD (n = 65) and typically developing boys (n = 41) following approved Institutional Review Board protocols. Three-dimensional coordinates were recorded for 17 facial anthropometric landmarks using the 3dMD Patient software. Statistical comparisons of facial phenotypes were completed using Euclidean Distance Matrix Analysis and Principal Coordinates Analysis. Data representing clinical and behavioral traits were statistically compared among groups by using χ2 tests, Fisher's exact tests, Kolmogorov-Smirnov tests and Student's t-tests where appropriate. RESULTS: First, we found that there are significant differences in facial morphology in boys with ASD compared to typically developing boys. Second, we also found two subgroups of boys with ASD with facial morphology that differed from the majority of the boys with ASD and the typically developing boys. Furthermore, membership in each of these distinct subgroups was correlated with particular clinical and behavioral traits. CONCLUSIONS: Boys with ASD display a facial phenotype distinct from that of typically developing boys, which may reflect alterations in the prenatal development of the brain. Subgroups of boys with ASD defined by distinct facial morphologies correlated with clinical and behavioral traits, suggesting potentially different etiologies and genetic differences compared to the larger group of boys with ASD. Further investigations into genes involved in neurodevelopment and craniofacial development of these subgroups will help to elucidate the causes and significance of these subtle facial differences.