Page 172 - My FlipBook

182 ANATOMY.
Nerves.—Branches from the inferior maxillary division of the fifth.
The External Pterygoid is a short, thick, conical muscle, extending
almost horizontally from the under surface of the great wing and the
pterygoid process of the sphenoid bone to the condyle of the inferior
maxilla and the interfibro-articulating cartilage of the temporo-maxil-
lary articulation. It arises by t^vo fleshy heads placed close together,
an inferior and a superior.
The Superior Head arises from the zygomatic surface of the great
wing of the sphenoid bone and the infratemporal ridge (pterygoid ridge)
which separates the temporal and zygomatic fossse.
The Inferior Head is the larger of the two, and arises from the outer
surface of the external plate of the pterygoid process and the tuberosity
of the palate and the superior maxillary bones.
The two heads soon unite, forming a short, stout muscle passing back-
ward and outward almost horizontally to be inserted by two portions,
superior and inferior.
The Superior Portion is inserted into the anterior portion of the inter-
articular tibro-cartilage of the temporo-maxillary articulation.
The Lower or Inferior Portion is attached to the depression on the
anterior surface of the neck of the lower jaw.
Relations.—On its outer surface the internal maxillary artery is
usually situated, passing between its two heads of origin : the buccal
nerves also come out between them. The ramus of the jaws and the
tendon of the temporal muscle are in relation with the outer surface.
The deep surface rests upon the upper part of the internal pterygoid
and the internal lateral ligament, the inferior maxillary nerve and mid-
dle meningeal artery. The superior border is crossed by the temporal
and masseteric branches of the inferior maxillary nerve.
Arteries.—The muscle is supplied by a branch from the middle or
second division of the internal maxillary.
Nerve.—Branch of the inferior maxillary (third division of the fifth).
Variations.—The external pterygoid sometimes receives a slip from
the temporal muscle.
The Pteri/r/oideus Proprius (Henle), not constant, is a longitudinal
cleavage of the upper portion of the external pterygoid, forming a band
of muscular and tendinous fibres, sometimes entirely tendinous, extend-
ing from the infratemporal crest over the external pterygoid muscle to
the lower and outer portion of the external pterygoid plate, or to the
tuberosities of the palate and superior maxillary bones. Occasionally
it sends a slip to the pterygo-maxillary ligament or to the lower jaw.
The Pterj/f/o-spinosus is a muscular strip occasionally found extend-
ing from the spine of the sphenoid bone to the jiosterior margin of the
external plate of the ptierygoid jjrocess, betMcen the two pterygoid mus-
cles. Sometimes this is replaced by a ligament, or even bone, leaving a
large foramen between the pterygoid and zygomatic fossse.
Action of the Mt'.scles of Masticatiox.—AVith the exception
of the external pterygoid^ these muscles act as elevators of the inferior
maxillary bono, and bring the teeth of the lower jaw forcibly into con-
tact with" the upper ; the muscles which antagonize them (those which
open the mouth) are of much less strength.