After our V’18 class passed the baptism of fire that was our small animal head exam, we all settled back with a sigh of relief, confident that the rest of the semester would be small beans compared to what we had already conquered. But we had another thing coming when we strolled into lab the next week and saw the rows of goat cadavers splayed out on tables and the pony cadavers swinging from individual racks. We became even more concerned when we learned that, besides dissecting both pony and goat, each lab was responsible for learning the information presented by student TAs assigned to the pig, cow, and alpaca. Five species?? Five species worth of differences in neck muscles, thoracic cavities, and abdominal organs? Spare us, please!
But it turned out to be really fun, following the path of ingesta as it travels through the gastrointestinal tract and learning how animals have adapted to their environment. For instance, llamas and alpacas have small salivary glands and so don’t make a lot of saliva. To compensate for the loss of the normal lubrication, suspension, and buffering provided by saliva, llamas and alpacas have ruminal glands. This is unusual, because the rumen in cows, goats, and sheep are aglandular and basically act as a fermentation vat, allowing the microbes to digest tough plant material. So the stinky green spit from an angry llama isn’t saliva—it’s actually ruminal fluid! Another GI adaptation is the equine ascending colon, which is greatly enlarged to maximize microbial fermentation of tough plant fibers, but whose twists and turns increase the probability of blockages and consequential colic.
I’m not saying that I ever want to memorize the locations of jejunal lymph nodes or the various cervical muscle fusions in each species ever again, but it was fascinating to finally get a look inside animals other than dogs and cats (pardon the pun).