J. Anat. (2001) 198, pp. 423–429, with 8 figures Printed in the United Kingdom 423 The course of the buccal nerve: relationships with the temporalis muscle during the prenatal period ! ! ! 1 1 1 J. R. ME! RIDA-VELASCO , J. F. RODRI! GUEZ-VAZQUEZ , C. DE LA CUADRA , J. A. MERIDA-VELASCO2 AND J. JIMENEZ-COLLADO1 " Departamento de Ciencias MorfoloT gicas II, Facultad de Medicina, Universidad Complutense, Madrid, # and Departamento de Ciencias MorfoloT gicas, Facultad de Medicina, Universidad de Granada, Granada, Spain (Accepted 17 October 2000) The aim of this study was to describe the course of the buccal nerve and its relationships with the temporalis muscle during the prenatal period. Serial sections of 90 human fetal specimens ranging from 9 to 17 wk development were studied by light microscopy. Each fetal specimen was studied on both right and left sides, making a total of 180 cases for study. A 3-D reconstruction of the region analysed in one of the specimens was made. In 89 cases the buccal nerve was located medial to the temporalis muscle; in 73 cases it penetrated the muscle; in 15 cases it lay in a canal formed by the muscle fibres and was covered by fascia, and finally, in 3 cases it was a branch of the inferior alveolar nerve. The study has revealed that in a large number of cases the buccal nerve maintains an intimate association with the temporalis muscle. Key words: Buccal nerve; temporalis muscle. in relation to anaesthesia of the oral region through which it extends (Jablonski et al. 1985; Hendy & The buccal nerve, a branch of the mandibular division Robinson, 1994) whereas others studied the surgical of the trigeminal nerve, carries sensory fibres which anatomy of the nerve (Bozola et al. 1989; Hendy et al. supply the lower buccal gingiva, lower buccal sulcus 1996) or described its course while carrying out and cheek mucosa and may also contribute to the surgical procedures (Singh, 1981; Vrionis et al. 1996). extra-oral cutaneous supply of the cheek (Hendy et al. Little attention has been given to the relationships 1996). Anatomy textbooks describe the course of the between the buccal nerve and the temporalis muscle buccal nerve as running between the 2 heads of the along its course. According to Harn & Shackelford lateral pterygoid muscle and then descending in a (1982), in adults the buccal nerve crosses the insertion forward direction in association with the maxillary of the temporalis muscle on to the mandible in a space artery and medial to the tendon of the temporalis containing lax connective tissue that is closed off by a muscle and Bichat’s fat pad to reach the external structure termed the fascial-tendinous complex. More- surface of buccinator (Gegenbaur, 1889; Testut & over, some authors found that occasionally the buccal Latarjet, 1980; Orts-Llorca, 1986; Williams, 1998; nerve penetrates the muscle or the tendon of the Rouvie' re & Delmas, 1999). temporalis muscle (Ge! rard, 1921; Hollinshead, 1962; Several authors have studied the buccal nerve from Romanes, 1987; Dubrul, 1990; Moore, 1993). The different perspectives. Some have focused on the objective of this work was to study the relationships relationships between the mandibular nerve and its between the buccal nerve and the temporalis muscle branches with aponeurotic structures in the region during the fetal period. This was done by analysing (Hovelacque & Virenque, 1913). Others authors have serial sections of human fetal specimens from 9 to examined the sensory distribution of the buccal nerve 17 wk of development. Correspondence to Prof. J. R. Me! rida-Velasco, Departamento de Ciencias Morfolo! gicas II, Facultad de Medicina, Universidad Com- plutense, 28040 Ciudad Universitaria, Madrid, Spain. Tel-fax: j34\1\394 13 39; e-mail: mvlopera!eucmax.sim.ucm.es 424 J. R. MeT rida-Velasco and others McManus & Mowry’s techniques (1968) for light microscopic study. A total of 90 human fetuses from the collection of the The region studied in specimen JR-1 (55 mm C-R Embryology Institute of the Complutense University length) was reconstructed according to the procedure of Madrid was studied. The specimens were between described by Arra! ez-Aybar et al. (1994). The images 35 and 150 mm crown-rump (C-R) length. All were generated by topographic techniques using the specimens had been previously conserved in neutral program AutoCAD V.14 for Windows 98. A standard formalin (10%). Sections with a thickness ranging PC was used with a 300 Hz Pentium II processor with from 15 to 25 µm depending on the size of the 128 Mb RAM, with a resolution of 800i600 and true specimen were cut. C-R length, plane of section, and colour images. weeks of development (O’Rahilly & Mu$ ller, 1996), are The photographs were first scanned with a HP- shown in Table 1. The slices were stained according to ScanJet 4s using a resolution of 300 dpi and a grey Table 1. Details of fetuses and planes of section examined C-R length Plane of Wk of C-R length Plane of Wk of Fetuses (mm) section development Fetuses (mm) section development Pe 35 Transverse 9 Cr-2 83 Transverse 13 OY-2 38 Frontal 9 HL-2 83 Transverse 13 OI-2 38 Sagittal 9 HL-31 83 Frontal 13 ABR 40 Frontal 9 B-107 84 Transverse 13 Faus 40 Sagittal 9 HL-32 84 Transverse 13 JR-3 43 Frontal 10 LR-1 84 Transverse 13 OC 43 Frontal 10 Sa-13 84 Transverse 13 VR-2 45 Frontal 10 Bu-23 85 Transverse 13 BE 47 Sagittal 10 RI-50 85 Transverse 13 Be-503 48 Frontal 10 N-12 85, 5 Transverse 13 Faus-7 48 Frontal 10 B-250 86 Transverse 13 PT-14 49 Frontal 10 J1 86 Sagittal 13 LR-5 50 Transverse 10 Be 501 87 Transverse 13 PT-7 51 Sagittal 10 Cr-1 87 Transverse 13 Ca-6 52 Frontal 11 B 608 90 Transverse 13 JR-1 55 Transverse 11 Cer 61 90 Transverse 13 G33 56 Transverse 11 B-54 91 Transverse 13 JP-1 56 Transverse 11 Sa-14 91 Transverse 13 Fe-21 57 Transverse 11 Ca-11 92 Sagittal 13 Mu-1 58 Transverse 11 Bu-18 93 Transverse 13 B-403 62 Frontal 11 B-207 95 Frontal 13 Cabeza 64 Frontal 11 B-72 95 Transverse 13 Be-101 65 Frontal 11 Te-1 96 Transverse 13 Bu-19 66 Transverse 12 B-195 97 Transverse 13 No-9 67 Frontal 12 Be 1011 97 Transverse 13 R-11 69 Transverse 12 B6 100 Transverse 14 Be 113 70 Frontal 12 Cu-1 100 Sagittal 14 Mu-10 70 Transverse 12 HC-1 100 Transverse 14 Bu-14 72 Transverse 12 Ca-8 101 Transverse 14 Mu-11 72 Transverse 12 Be 1010 103 Transverse 14 Mu-7 73 Transverse 12 J-4 103 Sagittal 14 HL 30 74 Transverse 12 Be 502 105 Transverse 14 Mu-5 74 Sagittal 12 St 8 105 Transverse 14 VR-2 74, 5 Frontal 12 NO 10 106 Transverse 14 B-25 75 Transverse 12 Bu 007 107 Frontal 14 Be-154 75 Transverse 12 Cer-78 110 Transverse 14 JR-8 75 Frontal 12 B62 113 Frontal 14 PT-12 75 Frontal 12 Ce-2 115 Transverse 15 Ca-7 76 Frontal 12 B-29 117 Transverse 15 Mat-1 77 Transverse 12 B3 120 Transverse 15 Esc 16 78 Transverse 12 R-6 125 Transverse 15 JR-6 80 Frontal 12 Cu-2 137 Frontal 16 Vr-3 80 Frontal 12 Esc-3 140 Transverse 16 Be-516 82 Sagittal 13 Do 144 Transverse 17 Be-3 83 Transverse 13 B-28 150 Transverse 17 Course of the buccal nerve 425 Fig. 1. Human fetus B-608 (90 mm CR; wk 13 of development). Transverse section. The temporalis muscle (T) inserts into the coronoid process of the mandible and extends along the 2 fascicles (arrows). One of these inserts on the anterior border of the ramus of the mandible and the other on the medial surface of the ramus. R, ramus of mandible; M, masseter; PL, lateral pterygoid; B, buccal nerve; L, lingual nerve; A, inferior alveolar nerve. Bar, 500 µm. Fig. 2. Human fetus Be-516 (82 mm CR; wk 13 of development). Sagittal section. The buccal nerve lies between the 2 heads of the lateral pterygoid muscle. At this level, the nerve gives rise to branches that supply the muscle (arrowhead). MA, mandibular nerve; B, buccal nerve; PL, lateral pterygoid muscle; PI, medial pterygoid muscle; T, temporalis muscle; C, Meckel’s cartilage; A, inferior alveolar nerve; R, ramus of the mandible; H, mylohyoid nerve. Bar, 500 µm. scale of 4 bytes with the program Visioneer PaperPort maximum precision and amplification of the details v. 3.0. The images were then rastered to bidimensional on the screen. As with wax sections, the height and vectors (x, y), using the cursor to trace the contours of real spatial location of each section was recorded (z). the images scanned onto the screen. This permitted After introducing all the vectors corresponding to 426 J. R. MeT rida-Velasco and others Fig. 3. Human fetus OY-2 (38 mm CR; wk 9 of development). Frontal section. The buccal nerve is located medial the temporalis muscle. B, buccal nerve; CP, coronoid process; M, masseter muscle; T, temporalis muscle. Bar, 500 µm. Fig. 4. Human fetus Be-501 (87 mm CR; wk 13 of development). Transverse section. The buccal nerve pierces the deeper fascicle of temporalis. B, buccal nerve; T, temporalis muscle; PL, lateral pterygoid muscle; CP, coronoid process.