At the level of medulla oblongata
- Along the midline of ventral surface of medulla oblongata a longitudinal fissure extends. It is called ventral median fissure. Lower end of fissure is continuous below with ventral median fissure of spinal cord. Upper end of fissure, at pontomedullary junction, ends in a small shallow depression called foramen cecum.
- On either side of ventral median fissure, there is a narrow linear elevation called pyramid with its broader upper end and narrower lower end. Deep to it, passes a descending (motor) tract called pyramidal tract (corticospinal tract). Some of the fibers of this tract decussate (cross) at the lower end of pyramid. Decussation of these fibers is visible at the lower end of ventral median fissure.
- Pyramid is demarcated laterally by anterolateral sulcus which is continuous below with same sulcus of spinal cord.
- An oval elevation, with its long axis being vertical, is present lateral to upper end of anterolateral sulcus. It is called olive. Deep to olive lies a mass of gray matter called inferior olivary nucleus
- Posterolateral to olive, a sulcus extends vertically which is parallel to anterolateral sulcus. This is called posterolateral sulcus. It is continuous below with same sulcus of spinal cord.
- Further posterolateral, a compact vertical band of medulla, passes upwards, backwards and laterally to cerebellum. It is called inferior cerebellar peduncle.
- Junction between pons and medulla oblongata presents a deep transverse sulcus. Midline of pontomedullary junction presents a small blind depression called foramen cecum.
- Along the midline of ventral surface of pons, a wide shallow sulcus extends vertically. It is known as basilar sulcus. Basilar artery passes along this sulcus from below upwards.
- On either side of basilar sulcus, ventral surface of pons presents a bulge, called basilar part of pons.
- Lateral to basilar part, pons presents thick compact band-like part which is horizontal in direction and passes laterally and backwards to cerebellum. This is middle cerebellar peduncle.
Ventral surface of midbrain presents bilateral, compact, thick band-like structures separated by a midline depression or broad sulcus. This is called cerebral peduncle. Upper cut surface of midbrain shows that cerebral peduncle is the part of midbrain which is ventral to aqueduct of Sylvius. Anterior most part of the cerebral peduncle is made up of compact bundle of descending (motor) fibers. This part is called crus cerebri.
Source: Easy and Interesting Approach to Human Neuroanatomy (Clinically Oriented) (2014)