Divided and reunited maxillary artery: developmental and clinical considerations.

We describe an anatomical variation of the right maxillary artery, discovered during dissection of a male human cadaver. The right maxillary artery bifurcates into unequal superficial (larger) and deep (smaller) divisions. Each division gives off several branches that distribute to the muscles of mastication, facial structures, and teeth. The superficial and deep divisions then reunite to form a complete loop, before giving off terminal branches in the pterygopalatine fossa. The entire arterial loop lies superficial to the branches of the mandibular nerve. This case provides further evidence for a network of vascular rings that surround soft tissue structures in the developing infratemporal fossa. Persistence of all or part of these rings determines adult anatomy. Extreme anatomical variations such as this one may complicate major procedures such as radical maxillectomy, as well as simple procedures such as inferior alveolar nerve blocks.

The evolution of dinosaur tooth enamel microstructure.

The evolution of tooth enamel microstructure in both extinct and extant mammalian groups has been extensively documented, but is poorly known in reptiles, including dinosaurs. Previous intensive sampling of dinosaur tooth enamel microstructure revealed that: (1) the three-dimensional arrangement of enamel types and features within a tooth-the schmelzmuster-is most useful in diagnosing dinosaur clades at or around the family level; (2) enamel microstructure complexity is correlated with tooth morphology complexity and not necessarily with phylogenetic position; and (3) there is a large amount of homoplasy within Theropoda but much less within Ornithischia. In this study, the examination of the enamel microstructure of 28 additional dinosaur taxa fills in taxonomic gaps of previous studies and reinforces the aforementioned conclusions. Additionally, these new specimens reveal that within clades such as Sauropodomorpha, Neotheropoda, and Euornithopoda, the more basal taxa have simpler enamel that is a precursor to the more complex enamel of more derived taxa and that schmelzmusters evolve in a stepwise fashion. In the particularly well-sampled clade of Euornithopoda, correlations between the evolution of dental and enamel characters could be drawn. The ancestral schmelzmuster for Genasauria remains ambiguous due to the dearth of basal ornithischian teeth available for study. These new specimens provide new insights into the evolution of tooth enamel microstructure in dinosaurs, emphasizing the importance of thorough sampling within broadly inclusive clades, especially among their more basal members.

An unusual variation of the flexor digitorum accessorius longus muscle--its anatomy and clinical significance.

In this article we describe a variant accessory muscle found in the deep posterior compartment of the leg in a 96 year-old female human cadaver. The flexor digitorum accessorius longus was found bilaterally, originating by two heads from the shafts of the tibia and fibula. The two heads of the muscle were observed to be subequal in size and none of the fleshy fibers of the muscle entered the tarsal tunnel. This stands in contrast with previous descriptions of accessory digital flexors, which are typically asymmetrical or single-headed, and which almost always introduce fleshy fibers into the tarsal tunnel. This variant structure has the potential to entrap the tibial nerve and compress the posterior tibial vessels either proximal to the talocrural joint or within the tarsal tunnel, and may be implicated in clinical scenarios involving imaging, surgery, compartment syndromes, or deep-vein thromboses.

Phylogenetic patterns of enamel microstructure in dinosaur teeth.

The tooth enamel microstructure of all the dinosaur taxa that are adequately represented in the American Museum of Natural History collections were analyzed using scanning electron microscopy. This study aims to determine whether or not better sampling within a major nonmammalian amniote (hereafter referred to descriptively as "reptile") clade will unearth phylogenetic patterns in enamel microstructure in addition to those dictated by tooth function. While interest in reptile enamel microstructure has increased in the past few years, intensive sampling focused on just one monophyletic reptile clade was not previously implemented. This study reveals that phylogenetic constraints play a larger role in shaping enamel microstructure in reptiles than previously thought. Within many monophyletic dinosaur clades the combination of enamel types and enamel features within a tooth-the schmelzmuster-is the same in all the taxa due to their common ancestry, and their schmelzmusters are diagnostic of their respective clades. While distantly related taxa with similar teeth and diets have similar schmelzmusters due to functional constraints, phylogenetic constraints keep those schmelzmusters distinct from one another. An interesting finding of this analysis is that the enamel complexity of a taxon does not necessarily coincide with the position of the taxon on a phylogenetic tree; more derived taxa do not necessarily have more derived enamel and more primitive taxa do not necessarily have more primitive enamel.