Snakes partition their body to traverse large steps stably.

Many snakes live in deserts, forests and river valleys and traverse challenging 3-D terrain such as rocks, felled trees and rubble, with obstacles as large as themselves and variable surface properties. By contrast, apart from branch cantilevering, burrowing, swimming and gliding, laboratory studies of snake locomotion have focused on locomotion on simple flat surfaces. Here, to begin to understand snake locomotion in complex 3-D terrain, we studied how the variable kingsnake, a terrestrial generalist, traversed a large step of variable surface friction and step height (up to 30% snout-vent length). The snake traversed by partitioning its body into three sections with distinct functions. Body sections below and above the step oscillated laterally on horizontal surfaces for propulsion, whereas the body section in between cantilevered in a vertical plane to bridge the large height increase. As the animal progressed, these three sections traveled down its body, conforming overall body shape to the step. In addition, the snake adjusted the partitioned gait in response to increase in step height and decrease in surface friction, at the cost of reduced speed. As surface friction decreased, body movement below and above the step changed from a continuous lateral undulation with little slip to an intermittent oscillatory movement with much slip, and initial head lift-off became closer to the step. Given these adjustments, body partitioning allowed the snake to be always stable, even when initially cantilevering but before reaching the surface above. Such a partitioned gait may be generally useful for diverse, complex 3-D terrain.

Surgical Excision of an Extratesticular Anaplastic Carcinoma in a Variable Kingsnake (Lampropeltis mexicana).

An adult male variable kingsnake (Lampropeltis mexicana) was presented for examination due to a three-week history of anorexia and obvious body deformities. On objective examination the animal was in poor condition, and on palpation, an intracoelomic mass was noted approximately in the distal third of the body, cranial to the cloaca. In agreement with the owner, an exploratory celiotomy was planned and performed and the mass was surgically removed. Modified Wright-Giemsa stain impression smears were taken, which were consistent with an undifferentiated tumour. Histological examination revealed the presence of a solid proliferation composed of highly tubular anaplastic cells and abundant multinucleated cells. The neoplastic cells were positive for cytokeratin (AE1/AE3), but not for vimentin. Periodic acid-Schiff (PAS) staining revealed the presence of large granular cells, which can be identified as the characteristic cells of the efferent ducts. Based on the morphological and immunohistochemical findings, the diagnosis of extratesticular anaplastic carcinoma was made. To the authors' knowledge, this type of neoplasm has never been reported in the male genital apparatus of snakes.