A rare variation of superior rectus muscle.

The extraocular muscles are responsible for all eye movements required to track and fix objects. Superior rectus muscle is located in the superior level of the orbital cavity, below musculus levator palpebrae superioris, tilted slightly to the lateral part of the orbit. In a routine dissection, we found a left, unilateral variation of the superior rectus muscle with no variation in other structures, such as nerves and vessels. The abnormal muscle presented in two parts - medial and lateral ones. The medial part bifurcated into two heads with different insertion points. It is a case of a rare variation of the extraocular muscles, which, to our knowledge, has not yet been reported.

H3 acetylation selectively promotes basal progenitor proliferation and neocortex expansion.

Increase in the size of human neocortex­acquired in evolution­accounts for the unique cognitive capacity of humans. This expansion reflects the evolutionarily enhanced proliferative ability of basal progenitors (BPs), including the basal radial glia and basal intermediate progenitors (bIPs) in mammalian cortex, which may have been acquired through epigenetic alterations in BPs. However, how the epigenome in BPs differs across species is not known. Here, we report that histone H3 acetylation is a key epigenetic regulation in bIP amplification and cortical expansion. Through epigenetic profiling of sorted bIPs, we show that histone H3 lysine 9 acetylation (H3K9ac) is low in murine bIPs and high in human bIPs. Elevated H3K9ac preferentially increases bIP proliferation, increasing the size and folding of the normally smooth mouse neocortex. H3K9ac drives bIP amplification by increasing expression of the evolutionarily regulated gene, Trnp1, in developing cortex. Our findings demonstrate a previously unknown mechanism that controls cortical architecture.