184 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 266. — The deep layers of the facial muscles, the buccinator, and the pterygoids, seen from the side. 

 The lower portion of the temporalis together with the coronoid process of the mandible has been removed; the whole 

 of the masseter is also removed and the parotid duct has been severed near its entrance into the buccinator. 



Fig. 267. — The left platysma, seen from the side. 



of the jaw, where it is inserted exactly opposite to the masseter. The outer surface of the muscle 

 is usually aponeurotic. 



[The pfcrygoideus internus is an elevator of the mandible, assisting the temporalis and masseter. The pterygoideus 

 externus draws the condyle of the mandible and the articular disc forward upon the articular eminence; when the muscle 

 of one side acts alone, it draws forward the mandibular condyle to which it is attached, the other one pivoting 

 in the mandibular fossa, and the result being an apparently lateral movement of the mandible. — Ed.] 



The muscles are supplied by the external and internal pterygoid nerves from the third division of the trigeminus. 



THE FASCIA OF THE HEAD. 



The parotideo-masseteric fascia (Fig. 260) is the layer of fascia which passes over the 

 parotid gland and the masseter muscle. At the zygoma it is connected with the temporal fascia, 

 at the anterior margin of the masseter with the buccopharyngeal fascia, and at the angle of 

 the jaw with the cervical fascia. 



The temporal fascia (Figs. 260 and 262) is the strongest fascia in the head and in its lower 

 portion divides into two layers, the superficial and the deep, which are separated by fatty tissue. 

 The interspace between the two layers becomes larger as they descend, the superficial layer 

 inserting into the anterior, the deep into the posterior border of the zygoma. The upper cir- 

 cumference of the temporal fascia is connected with the galea aponeurotica. 



The anterior portion of the buccopharyngeal fascia lies upon the buccinator and is connected 

 with the parotideo-masseteric fascia; the posterior portion is stronger, more tendinous, and 

 covers the inner surface of the pterygoideus internus. In this posterior portion are embedded the 

 pterygomandibular raphe (ptcrygomaxillary ligament) and the stylomandibular (stylom axillary) 

 ligament (see page 118). In this situation the fascia forms the postero-lateral wall of the oral 

 cavity and the lateral wall of the pharynx. 



[The cranial musculature, considered from the developmental standpoint, includes several muscles in addition to 

 those which are assigrMpto the head in the above description, since it is properly to be regarded as consisting of all the 

 muscles supplied by the cranial nerves. Among these nerves there exist motor fibers of two different qualities: (i) lateral 

 motor roots whose nuclei of origin may be regarded as occupying a position intermediate between the sensory nuclei and 

 (2) the median motor roots, which correspond in all their essentials to the anterior roots of the spinal cord. The lateral 

 motor roots, which occur in connection with the fifth, seventh, ninth, tenth, and eleventh nerves, are distributed to the 

 muscles associated with the embryonic branchial arches, while the median motor roots are represented by the third, 

 fourth, sixth, and twelfth nerves, and supply the muscles associated with the eyeball and tongue. 



In accordance with this difference of innervation, which is of great morphological importance, the cranial muscula- 

 ture may be divided into two groups: (i) The myomeric muscles, supplied by median motor roots, and (2) the branchi- 

 omcric muscles, supplied by lateral motor roots. The muscles belonging to the former group as well as certain of those 

 belonging to the branchiomeric group, such as the muscles of the tympanum, palate, pharynx, and larynx, will be described 

 and figured in connection with the regions to which they belong, but for the sake of completeness they will 

 be included in the classification that follows. In the classification of the muscles of each group the individual nerve- 

 supply may form the basis. 



