Deep Dissection of Suboccipital Triangle Musculature. Overlying trapezius, splenius capitis, and semispinalis capitis muscles have been removed to expose the deep lying suboccipital muscles. Here, the spinous process of the axis (C2 vertebra) and transverse processes and posterior tubercle of the atlas (C1 vertebra) are in view with associated musculature. Several muscles attach to the spinous process of C2, including the semispinalis cervicis, obliquus capitis inferior, and rectus capitis posterior major. The obliquus capitis inferior muscle attaches laterally to the transverse process of the atlas. From here arises the obliquus capitis superior, which inserts into the lateral part of the inferior nuchal line. The rectus capitis posterior major muscle converges on the obliquus superior attaching just medial to it. These three muscles form the boundaries of the suboccipital triangle, the floor of which contains the atlantic portion of the vertebral artery and the suboccipital nerve supplying motor innervation to the suboccipital muscles. The rectus capitis posterior minor muscles arise from the posterior tubercle of C1 and attach superiorly to the medial part of the inferior nuchal line. The longissimus capitis muscles are seen attaching to the mastoid process of the temporal bone. The occipital artery is a branch of the external carotid artery. It is shown here having passed deep to the splenius capitis and penetrating the semispinalis capitis. It normally passes through the trapezius muscle to supply the posterior scalp. (Image courtesy of PA Rubino)