Associate Professor NYITCOM at Arkansas State University Jonesboro, Arkansas, United States
Abstract Body : Lizards continue to grow in popularity within both the pet trade and in scientific studies. A greater understanding of their anatomy is necessary to ensure proper veterinary care for these exotic animals. One area of interest for both herpetology and herpetoculture is the vascular system and its function in thermoregulation of the animals. Previous research on lizard vasculature has been limited to the large squamate group, Iguania. There has yet to be similar investigations into the vasculature of the more speciose group, Scleroglossa. Our study seeks to expand our knowledge of squamate vascular anatomy by describing the vascular patterns within the head of an adult savannah monitor lizard (Varanus exanthematicus). We injected a post-mortem specimen with BriteVu contrast agent to visualize the arteries and veins under µCT. The specimen later underwent a diceCT treatment to visualize the remaining soft tissues, allowing us to describe the in-situ pathways of these vessels more accurately. We compared the vascular pathways in our monitor lizard to previously published studies on iguanas. Our observations uncovered conserved areas of the vascular pathway near the base of the skull, such as the branching of the mandibular artery from the temporoorbital artery and the primary source of cephalic vasculature coming from the internal carotid artery. Varanus differs from iguanas in having relatively longer temporoorbital and mandibular arteries with more reduced supraorbital, palatine, and sphenopalatine arteries. The well-developed palatal plexus and orbital sinus observed in iguanians has been implicated in regulating brain and eye temperature within tolerable levels via actions such as gular panting. We did not observe the presence of either the plexus nor the orbital sinus in our monitor lizard. Instead, we observed most of the vasculature for the palate being supplied by branches of the maxillary artery, and an extensive vascular plexus along the nasal passages. The lack of a palatal plexus in Varanus coincides with the lack of panting behavior and the specialized tongue functions observed in this group. We suspect cephalic cooling in monitor lizards is accomplished via the more elaborated nasal-vascular system.
