CRANIO-MANDIBULAR MUSCLES 341 



The sigmoidal septum is a thin membrane which occupies the incisura mandibulse and sepa- 

 rates the masseter from the external pterygoid muscle. 



MUSCLES 



The temporalis (fig. 345). — Origin. — (1) From the whole of the temporal fossa, with the 

 exception of that part formed by the body and temporal process of the zygomatic (malar) bone; 

 and (2) from the fascia covering the fossa. Insertion is into the tip, dorsal and ventral borders, 

 and the whole internal surface of the coronoid process of the mandible and the ventral portion 

 of the medial surface of the ramus. 



In structure, the muscle is thin near its superior margin, but becomes thick as its insertion 

 is approached. The fibre-bundles arising from the medial surface of the fossa and from the 

 fascia converge upon the medial and lateral surfaces and the margins of a thick, broad tendon 

 which begins very high in the muscle, becomes visible laterally some distance above the zygo- 

 matic arch, and is inserted into the tip, edges, and internal surface of the coronoid process. On 

 the ventral and dorsal margins of the tendon the insertion of fibre-bundles continues to the coro- 

 noid process, while medially the insertion of the fibre-bundles is continued on the medial surface 

 of the coronoid process and often on the ramus as far as the body of the bone. 



Nerve-supply. — Usually three branches from the anterior branch of the mandibular division 

 of the fifth nerve curve upward over the temporal surface of the great wing of the sphenoid and 

 enter the deep surface of the muscle. The posterior and middle nerves pass above the external 

 pterygoid; the anterior, which springs from the buccinator nerve, passes between the two heads 

 of the external pterygoid before curving upward. 



Relations. — The muscle is covered by the temporal fascia and the zj-gomatic arch. Below 

 the temporal fossa the pterj^goid muscles and the buccinator lie medial to it. The temporal 

 fossa in front of the muscle is filled with a fatty areolar tissue and this also extends between the 

 muscle and the temporal fascia. Fatty tissue hkewise lies between the muscle and the buccina- 

 tor. Medial to the muscle run the deep temporal vessels and nerves, the buccinator nerve 

 and the spheno-mandibular ligament. The masseteric nerve passes lateralward behind and 

 below the tendon. 



The masseter (fig. 343) is composed of two layers. The superficial layer arises bj^ an apo- 

 neurosis from the anterior two-thirds of the lower border of the zygomatic (malar) bone. The 

 fibre-bundles arise from the deep surface of this aponeurosis and its tendinous prolongations 

 pass obliquely downward and backward, and are inserted into the lower half of the external 

 surface of the ramus, into the angle, and into the neighbouring portion of the body of the man- 



FiG. 347.* — A AND B ARE Transverse Sections and C (after Testut), a FRorfrAL Section 



THROUGH the LeFT SiDE OF THE HeaD, IN THE REGIONS INDICATED IN THE DIAGRAM. 



a and b in the diagram indicate the regions through which pass sections A and B, fig. 351; and 



a^, section A, fig. 357. 



1. Adipose tissue. 2. Arteria temporalis superficialis. 3. A. carotis externa. 4. A. car- 

 otis interna. 5a. A. maxillaris externa (facial) . 56. A. maxillaris interna. 6. A. verte- 

 bralis. 7. Atlas. 8. Cerebellum. 9. Epistropheus (axis). 10. Fascia buccopharyngea. 

 11. F. cervicaUs, a (superficial layer), b, deep parotid process. 12. F. interpterygoidea. 

 13. F. masseterica. 14. F. nuchae. 15. F. pharyngobasilaris. 16. F. pharyngis lateralis. 

 17. F. temporahs. 18. Galea aponeurotica. 19. Glandula parotica. 20. Ligamentum stylo- 

 mandibularis. 21a. Mandible, capitulum; b, coronoid process. 22. Meatus acusticus 

 ext. 23. Medulla oblongata. 24. Medulla spinalis (spinal cord). 25. Musculus auricu- 

 laris posterior (retractor auris). 26. M. buccinator. 27. M. caninus (levator anguli 

 oris). 28. M. constrictor pharyngis medius. 29. M. constrictor pharyngis superior. 30. 

 M. digastricus. 31. M. genio-glossus. 32. M. hyo-glossus. 33. M. incisivus labii 

 inferioris. 34. M. levator veh palatini. 35. M. longus capitis (rectus capitis anticus 

 major). 36. M. longissimus capitis (trachelo-mastoid). 37. M. longitudinalis inferior. 

 38. M. masseter. 39. M. mylo-hyoideus. 40. M. nasalis (alar portion). 41. M. 

 obliquus capitis inferior. 42. M. obhquus capitis superior. 43. M. pterygoideus externus 

 — a, superior fasciculus; b, inferior fasciculus. 44. M. pterygoideus internus. 45. M. 

 quadratus (levator) labii superioris. 46. M. rectus capitis anterior (minor). 47. M. 

 rectus capitis posterior major. 48. M. rectus capitis posterior minor. 49. M. rectus 

 capitis lateralis. 50. M. semispinalis capitis (complexus). 51. M. spleniiLs capitis. 

 52. M. sterno-cleido-mastoideus. 53. M. stylo-glossus. 54. M. stylo-hyoideus. 55. 

 M. stylo-pharyngeus. 56. ]M. temporalis (a, fasciculus from zygoma). 57. M. tensor 

 veh palatini. 58. M. trapezius. 59. M. zygomaticus (major). 60. Xervus accessorius 

 (spinal accessory). 61. N. alveolaris inferior (dental). 62. N. alveolaris posterior superior 

 (dental). 63. N. auriculo-temporalis. 64. X. buccinatorius. 65. N. canahs pterygoidei 

 (Vidian nerve). 66. X. glosso-pharyngeus. 67. X. hypoglossus. 68. X. lingualis. 

 69. X. mandibularis. 70. N. masseteric nerve. 71. X. maxillary nerve. 72. X. mylo- 

 hyoid nerve. 73. X. palatinus. 74. Sym.pathetic trunk. 75. X. temporalis profundus. 

 76. X. vagus. 77. Os occipitale — a, basilar portion; b, external protuberance. 78. Os 

 sphenoidale. 79. Os temporale — a, processus zygomaticus; b, tubercle. 80. Os zygo- 

 maticum (malar). 81. Pharyngeal orifice of tuba auditiva (Eustachian tube). 82. 

 Palatum durum (hard palate). 83. Pharynx — a, oral portion; b, nasal portion. 84. 

 Pharyngeal recess. 85. Sinus maxillaris (antrum of Highmore). 86. Sinus transversus 

 (lateral). 87. Tonsila palatina. 88. Uvula. 89. Vena faciahs posterior (temporo- 

 maxillary). 90. V. jugularis interna. 

 * This and the following series of cross-sections are taken from a thin, not very muscular, 



adult male. The fasciae are represented in most instances disproportionately thick. 



