THE INFERIOR DENTAL AND LINGUAL NERVES. 247 



Inferior dental nerve. The inferior dental or mandibular nerve (n. alveolaris 

 inferior} is the largest of the branches of the lower maxillary nerve. It descends 

 under cover of the external pterygoid muscle, behind and to the outer side of the 

 lingual nerve, and, passing between the ramus of the jaw and the internal lateral 

 ligament of the temporo-maxillary articulation, enters the inferior dental canal. 

 In company with the dental artery, it proceeds along this canal, and supplies 

 branches to the teeth. At the mental foramen it bifurcates ; one part, the incisor 

 branch, being continued onwards within the bone towards the middle line, while the 

 other, the much larger mental branch, escapes by the foramen to the face. 



AVhen about to enter the foramen on the inner surface of the ramus of the jaw, 

 the inferior dental nerve gives off the slender mylo-hyoid branch. 



Branches. (a) The mylo-hyoid branch descends in the groove on the inner side 

 of the ramus of the lower jaw to the under surface of the mylo-hyoid muscle, to 

 which and to the anterior belly of the digastric it is distributed. The fibres of this 

 nerve may be traced back within the sheath of the inferior dental to the motor root 

 of the inferior maxillary nerve. 



(b) The dental branches supply the molar and bicuspid teeth, together with the 

 adjoining part of the gum. They form by their communications a fine inferior 

 dental plexus, resembling that formed by the corresponding nerves in the upper jaw. 



(c) The incisor branch continues the direction of the trunk of the nerve, and 

 supplies filaments to the canine and incisor teeth. 



(d) The mental or labial nerve, emerging from the bone by the mental foramen, 

 divides beneath the depressor anguli oris into three parts, an inferior, which descends 

 to the integument of the chin, and two superior, which ascend to the skin and 

 mucous membrane of the lower lip. All three communicate freely with the 

 mandibular branch of the facial nerve. 



Varieties. The inferior dental and lingual nerves have been observed to form a single 

 trunk as far as the dental foramen. On the other hand, they are often separated by an 

 accessory ligament stretched between the external pterygoid plate and the spine of the 

 sphenoid, to the outer side of the pterygo-spinous ligament (see v. Brunn, op. cit. p. 244). 

 The inferior dental nerve is occasionally perforated by the internal maxillary artery. It 

 sometimes has one or two accessory roots from other divisions of the inferior maxillary. The 

 most common of these is one which arises from the G-asserian ganglion and remains separate 

 until after it enters the dental canal (lesser inferior dental nerve, Sapolini). 



The mylo-hyoid nerve frequently (constantly, Sappey) gives off a small branch, which 

 pierces the mylo-hyoid muscle and joins the lingual nerve. Branches are also described as 

 passing from the mylo-hyoid nerve to the depressor anguli oris and platysma myoides muscles 

 (Herile), to the integument below the chin (Krause, Schwalbe, and others), and to the sub- 

 maxillary gland (Meckel, Henle, Curnow). 



Lingual nerve. The lingual branch descends under cover of the external 

 pterygoid muscle, lying to the inner side and in front of the dental nerve, and 

 generally united to that by a cord which may cross over the internal maxillary 

 artery. Near its origin, it is joined at an acute angle by the clwrda tympani, a 

 small branch which is given off by the facial nerve, and descends from the inner 

 end of the Glaserian fissure. It then passes between the internal pterygoid muscle 

 and the ramus of the lower jaw, and is inclined obliquely inwards to the side of the 

 tongue, over the upper constrictor of the pharynx (where this muscle is attached to 

 the jaw), and above the deep portion of the submaxillary gland. Lastly, the nerve 

 crosses below "VVharton's duct, and is continued along the side of the tongue to the 

 apex, lying immediately beneath the mucous membrane. 



Branches. (a) Communicating brandies. In addition to the cord above men- 

 tioned passing from the inferior dental to the lingual nerve, and the connection with 

 the facial nerve through the chorda tympani, the lingual nerve gives off branches to 



