This section is from the book "Anatomy Of The Arteries Of The Human Body", by John Hatch Power. Also available from Amazon: Anatomy of the Arteries of the Human Body, with the Descriptive Anatomy of the Heart.
The Anterior Spinal Artery arises from the vertebral near its termination; sometimes from the inferior artery of the cerebellum, or even from the basilar trunk. It descends in a tortuous manner, and unites with its fellow from the opposite side at the anterior margin of the foramen magnum, at the lower extremity of the medulla oblongata, so as to form a single trunk larger than either of the posterior spinal arteries: this common trunk descends tortuously in front of the spinal marrow, below which it is prolonged, without subdividing, through the centre of the Cauda equina, till it reaches the sacro-coccygeal articulation, and here it terminates in anastomosing with the sacral arteries. In this course it gives off branches which anastomose with the lateral spinal branches of the vertebral, ascendens colli, and cervicalis profunda arteries which pass through the spinal foramina; and with minute branches given off from the artery of the opposite side: this artery sends many branches to the pia mater, and some very delicate branches to the spinal marrow. It may be observed that as the vertebral arteries converge superiorly to form the basilar trunk, and the anterior spinal arteries converge inferiorly to form a common trunk, the four arteries necessarily include a lozenge-shaped space in front of the medulla oblongata.