Different textbooks define the submandibular space - a potential space around the mandible associated with odontogenic infections - differently.
The 9th edition of Last's Anatomy, as well as many ENT textbooks, define the submandibular space as extending from the mucosa at the floor of the mouth down inferiorly to the investing layer of fascia. Bordered laterally by mandible and medially by muscles of the tongue. It is then described as having two subsets one above the mylohyoid muscle, the sublingual space, and one beneath termed the submaxillary.
However, confusingly, other textbooks described simply the sublingual space, and then call the submaxillary space (last's) the submandibular space.
We have adopted last's definition because it's a prescribed bords text.
The submandibular space extends between the mucosa of the floor of the mouth down to the investing layer of fascia, bordered anteriorly and laterally by the mandible and medially by muscles of the tongue (hygoglossus and styloglossus).
Posterioinferiorly the submandibular space communicates with the parapharyngeal or lateral space.
The submaxillary space (submandibular in other books) is coronally defined by a triangle; the mandible laterally forming an apex with the mylohyoid medially and an inferior covering of investing fascia, platysma, superficial fascia and skin.
It contains the superficial part of the submandibular gland and the facial artery and vein.
It has a free posterior border around which the submandibular gland wraps to have a small section of the gland sitting in the sublingual space from which the submandibular duct projects forward.