Tree Shrew brain
Photos and text: Terence Mitchell
Starting from an existing edge of loose skin, use the rat-tooth forceps to gently pull the skin off of the head. Use scissors to cut the skin into manageable pieces. Remove the temporalis muscle and muscles of the neck. Using the sharp probe, make a hole just caudal to the external occipital protuberance. Use the smallest scissors available to cut around the skull starting at the occipital protuberance. Keep the deep edge of the scissors pressed against the skull so as not to damage the soft tissue beneath. Much of the dura mater may come off with the skull. Remove any remaining dura and its projections between the cerebral hemispheres, falx cerebri, and the tentorium cerebellum between the cerebrum and cerebellum. Using a small spatula, you should be able to lift the brain out of the skull. Begin removing the brain anteriorly as this section is not as strongly attached as the posterior. Do this slowly, watching for any cranial nerves or major vessels as you remove the brain. It is much easier to see these tiny structures before they are cut.
Unfortunately, the tree shrew's brain was not well preserved. The superficial ventral surface and most of the midbrain were particularly decomposed, and I could not identify many individual structures. I could not see the cranial nerves or major vessels either leaving the brain or passing through the skull, because of the poor state of the soft tissue in this area. I have identified a few structures in a mid-sagittal section, Figure 1. On your cadaver, note the smooth texture of the cerebrum.
As a part of his detailed work on tree shrew anatomy Le Gros Clark dissected the brain of Tupaia minor, and compared his findings with those for the brains of an elephant shrew, Macroscelides, and an insectivore, Lipotyphla [1]. For the most part the tree shrew brain was similar to these species. However, the cerebral hemispheres were longer, the occipital lobe was larger, the olfactory bulbs were reduced, and the visual cortex was more complex. Le Gros Clark concludes that T. minor differs from other insectivorous mammals in specific characters, which make it similar to primates. While this result is certainly interesting, it is possible that as the database of neuroanatomy for other mammals grows many of these similarities may prove to be primitive. Many of these differences may be adaptations to a diurnal activity pattern. Tupaia belangeri and all tree shrews, excluding Ptilocercus lowii, are diurnal. This fact could account for the reduction of the olfactory bulbs, and the increase in areas associated with vision.
1. Le Gros Clark, W.E.1924. On the brain of the tree shrew (Tupaia minor).
Proceedings of the Zoological Society of London 1924: 559-567.
Le Gros Clark, W.E.1926. On the anatomy of the pen-tailed tree shrew
(Ptilocercus lowii). Proceedings of the Zoological Society of London
1926: 559-567.
to Comparative Mammalian Anatomy home
to tree shrew facial and head musculature