During the Middle Ages, it was assumed that man was a microcosm of the universe and, as a result, medieval society merged the art of Astrology with a wide variety of practices and sciences such as Alchemy, Medicine or Natural Philosophy, in order to provide valuable and reliable explanations for different phenomena. However, it was in the medical field that Astrology reached its greatest development, and it resolved into a highly esteemed practice whose foremost aim was to diagnose a sickness, administer the appropriate treatment and determine its outcome.
The main idea that lies at the core of astrological Medicine is the widespread credence that the planets, together with the Sun and the Moon and the signs of the Zodiac, exerted thorough power and governed the different organs and parts of human anatomy. The body was divided into twelve houses, and since there are twelve zodiac signs, each one together with the influence of the seven planets played a crucial role ruling the different parts of human body.
The connection of each sign with particular organs and limbs is closely related to the animals associated to them, and constructed upon the idea of shared virtues or characteristics. That is why Scorpio is linked to the “secret parts”, because the power and strength of scorpions is located in their tail. Leo is represented by a lion whose vigour is to be found in the heart and as a result, it is connected to the chest.
Consequently, it is possible to find a large number of medieval manuscripts containing prognostic treatises where this material relating to astrological Medicine was gathered. A wide range of these texts were translations from Greek, Hebrew and Arab scholars that reached the Latin West in the fourteenth and fifteenth centuries. As a result, physicians won access to a great variety of medical astrological writings that circulated in England in the late Middle English period, both in Latin and in vernacular translations, until the end of the fifteenth century. 
One of these late Middle English prognostic treatises can be found in the University of Glasgow Library’s MS Hunter 513: Pseudo-Hippocrates’ Treatise on Zodiacal Influence (ff. 98r – 104r). The treatise opens with its attribution to Hippocrates, which is followed by an explanation of its main purpose: to indoctrinate about the influence of the planets as far sicknesses and their outcome – life or death – are concerned, as well as to offer a training regarding prescriptions.
The manuscript tells us that there are three main points that ought to be taken into account prior to a treatment. First of all, to observe the moon thoroughly; secondly, to be aware of the time when the disease was contracted; and finally, to know in which sign of the Zodiac it falls. After that, the structure of the treatise is provided, explaining that it provides an overview of each of the twelve signs of the Zodiac from this medical astrological perspective.
Each discussion of the twelve signs of the Zodiac is structured in a similar way. They are addressed in the following order: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. First of all, the sign is defined according to its prime qualities and anthropomorphic characteristic. They are then associated with the planets which share the same qualities and also to the specific part of the body where the disease is likely to appear. After that, the ailments the patient is likely to suffer from are mentioned, as well as his life expectancy. Finally, the right moment to apply a treatment is elucidated with an explanation of the remedy.
This pattern is repeated with little variation among all the signs, and therefore it is possible to acquire a general overview of the whole treatise from a single example: Aries. This is a hot and dry sign related to fire. As a result, when Mars or the Sun which have its same qualities are present, the sickness will appear in the head, leading to fevers and delirium. If Saturn is close to the Moon, the patient will die in eight days. However, if Saturn and Mars are not next to the Moon at that point, it is the right moment to administer a treatment, thirteen days after the disease was contracted. The remedy consists of letting the pattient bleed from the vein of the heart and of taking cold medicines with food and drinks.
Therefore, it is essential to know one’s horoscope in order to be able to carry out a proper diagnosis and establish an efficient treatment. So please, do not hesitate to read Hunter MS 513 (f. 98r-104r) for further information on your medieval horoscope!
 Irene Diego-Rodríguez (email@example.com) wrote her master thesis on Hunter MS 513 at Glasgow University and is currently working on her Ph.D. which aims to identify all the Zodiacal Lunaries entitled Þe Booke of Ypocras in late Middle English manuscripts in order to carry out a linguistic and paleographic study: https://uah-es.academia.edu/IreneDiegoRodr%C3%ADguez
 For further information on the translation of this kind of prognositc treatises see De la Cruz-Cabanillas, Isabel and Irene Diego-Rodríguez ” Astrological Medicine in Middle English: The Case of Þe Booke of Ypocras “. Textual Reception and Cultural Debate in Medieval English Studies. Cambridge Scholars, 2018, pp. 79-99.