The mylohyoid muscle is a small, flattened muscle whose morphology is predominantly quadrilateral and which, together with the contralateral muscle of the same name, forms the muscular floor of the mouth. Due to its location, it belongs to the group of neck muscles, which are subclassified into three groups.
These three groups are: an anterolateral muscle group, an anterior muscle group, and a posterior muscle group. At the same time, the anterior muscle group is divided topographically into muscles of the deep plane and muscles of the superficial plane.
Mylohyoid muscle (left)
The muscles of the superficial plane are separated by the hyoid bone into a suprahyoid group (those located above the hyoid bone) and an infrahyoid group (located below the hyoid bone). The mylohyoid muscle is located above the hyoid bone in a median plane; then belongs to the group of suprahyoid muscles.
It separates the sublingual space from the submandibular space, forming with the hyoglossus muscle a space called the sublingual cell. The sublingual and submandibular spaces communicate within the posterior border of the mylohyoid. This is considered a pharyngeal muscle, since it originates embryologically in the first pharyngeal arch or branchial arch.
Origin and insertion
Before describing the origin and insertion of the mylohyoid muscle, some structures of the mandible - also known as the lower maxilla - should be briefly described in order to properly locate the origin and insertion of the muscle.
An oblique line is located on the posterior aspect of the mandible bone that crosses the internal aspect of the body of the lower jaw, which runs from the center of the body towards the anterior border of the ramus on each side. This line is called the internal oblique line or mylohyoid line.
In this way, the insertion of origin is located above, in the mylohyoid line or internal oblique line of the lower jaw; from there the fibers are directed downward and toward the center.
In the center it has the characteristic of joining the contralateral mylohyoid muscle by a mid-suprahyoid aponeurotic raphe. This characteristic makes both muscles together form the floor of the mouth proper.
Downwards it inserts into the body of the hyoid bone with approximately one third of its fibers. The fibers of this quadrilateral muscle are diverse in length.
The most medial fibers are shorter and go directly from the internal oblique line to the mid raphe, approximately two-thirds of their fibers, and as they become more lateral, they are longer. Its posterior fibers go from the internal oblique line directly to the body of the hyoid bone.
Mylohyoid muscle relationships
Towards the center it relates to its counterpart on the opposite side in the suprahyoid mid raphe, forming an open channel above and behind.
Downward or superficial, its face is convex and relates to the anterior bellies of the digastric muscle on each side. Upward, its face is concave and relates directly to the oral cavity.
Its posterior border is related to the antero-internal extension (or uncinate extension) of the submaxillary gland, which accompanies Wharton's canal.
In these relationships one of the main triangles of the neck is delimited: Pirogoff's triangle. This is delimited by the posterior border of the mylohyoid muscle in front, the intermediate tendon of the digastric muscle below, and the hypoglossal nerve above.
Pirogoff's triangle is important because the lingual artery (behind the hyoglossus muscle) and the superficial lingual vein pass through it.
Function
From a functional point of view, they belong to the group of muscles of chewing or swallowing. The chewing muscles are a group of muscles that allow the jaw to be moved in various directions so that it can perform the function of chewing.
In this sense, the posterior (lateral) fibers of the muscle allow lateral movements to the jaw, while its anterior fibers allow lifting and lowering movement when acting in conjunction with other muscles of mastication.
Similarly, it elevates the hyoid bone and tongue and, as mentioned above, strengthens the floor of the mouth.
Irrigation
The external carotid artery is one of the terminal branches of the common carotid artery. It branches into six collateral branches: superior thyroid artery, facial artery, lingual artery, occipital artery, ascending pharyngeal artery, and posterior auricular artery. In addition, it contains two terminal branches, which are the maxillary artery and the superficial temporal artery.
The supply of the mylohyoid muscle is mainly provided by ascending and descending branches of the submental artery, which is a cervical collateral branch of the facial artery which, in turn, is also a collateral branch of the external carotid artery.
Similarly, it receives blood supply from the mylohyoid artery, a branch of the inferior alveolar artery, which originates as a descending collateral branch of the maxillary artery, which is also a terminal branch of the external carotid.
In conclusion, the external carotid artery supplies the mylohyoid muscle through collateral branches and terminal branches. Venous circulation is provided by the mylohyoid vein, which joins the inferior dental vein to open into the pterygomaxillary venous plexus.
Innervation
The trigeminal nerve (5th cranial nerve) is a mixed, motor and sensory nerve that is divided into three main branches: ophthalmic nerve, maxillary nerve, and mandibular nerve.
The mandibular nerve is the largest branch of the trigeminal nerve, it has multiple collateral branches and ends in two terminal branches: the inferior alveolar nerve and the lingual nerve.
The inferior alveolar nerve branches to give rise to the mylohyoid nerve, which provides motor innervation to the mylohyoid muscle and the anterior belly of the digastric muscle. This mylohyoid nerve descends with the homonymous artery into the mylohyoid sulcus to supply and supply the floor of the mouth.
References
- Neurorehabilitation service. Musculature involved in swallowing. February 18, 2015. Recovered from: neurorhb.com
- Neck issues. Anatomy of the submaxillary, sublingual, and minor salivary glands. Recovered from: otorrinoweb.com
- Latarjet Ruiz Liard. Human Anatomy 4th Edition. Editorial Panamericana. Volume 1. Neck muscles. P. 131.
- Franks H. Netter, MD Atlas of Human Anatomy. 3rd Edition. Editorial Elsevier. Plates 24-25, 27-29, 410.
- Torsten Liem, Cranial Osteopathy (Second Edition). In: Chapter 12 - The orofacial structures, pterygopalatine ganglion and pharynx. Elsevier, 2004. Pages 437-484