FACIALIS MUSCULATURE 329 



side into two laj'ers which ensheath the sterno-cleido-mastoid and trapezius muscles. As a 

 free fascia it is attached to the lower jaw, to the clavicle and sternum, and to the hyoid bone 

 which divides it into a submaxillary and an infra-hyoid portion. It is connected with the fibrous 

 sheath of the parotid and submaxillary glands. The middle laj-er of cervical fascia is composed 

 of two laminae, one extending between the sterno-hyoid and omo-hyoid and another more deli- 

 cate one beneath this, ensheathing the thyreo-hyoid and sterno-thyreoid muscles and fused with 

 the fibrous sheath which encloses the carotid artery, internal jugular vein and the vagus nerve. 

 The deeper muscles of the side and front of the neck and the intrinsic muscles of the back of 

 the neck are hkewise ensheathed by muscle fasciae. 



Of the various groups of muscles mentioned above, some, for the sake of con- 

 venience, are treated in connection with the organs to which they belong. Thus 

 the muscles of the eye and ear are taken up in Section VIII; those of the palate, 

 pharynx and larynx in Sections IX and X; the deep dorsal musculature of the 

 neck will be taken up in the section on the intrinsic muscles of the back, p. 410, 

 The remaining groups of muscles will be taken up in the following order: — 



1. The facial group p. 329. 



2. The cranio-mandibular group p. 338. 



3. The supra-lwoid musculature p. 343. 



4. The muscles of the tongue p. 345. 



5. The superficial shoulder-girdle musculature p. 347. 



6. The infra-hyoid musculature p. 350. 



7. The scalene musculature p. 353. 



8. The prevertebral musculature p. 355. 



9. Anterior and lateral intertransverse muscles p. 356. 

 10. Deep musculature of the shoulder girdle p. 356.* 



1. THE FACIALIS MUSCULATURE 



(Figs. 341, 344) 



The muscles of this group are intimately connected with the scalp, with the 

 skin of the face and neck, and with the mucous membrane lining the lips and the 

 cheeks. Most of the muscles have an osseous origin and a cutaneous insertion, 

 but there are exceptions. Both origin and insertion may be cutaneous, or the 

 attachment msiy be to an aponeurosis instead of directly to the skin. The 

 deeper musculature about the mouth is attached to the mucous membrane. 



The muscles are composed of interdigitating muscle-fibres which are grouped 

 in bundles that take a nearly parallel or slighth' converging course and give rise 

 to thin muscle-sheets. The extent of development of the various muscles of the 

 group and their independence varies greatly in different individuals. 



The region from which the facial musculature originates in the embryo is, in the main at 

 least, that of the hyoid arch immediately below the ear. From here the musculature spreads 

 with the development of the facial nerve, dorsalh^ to the occipital region behind the ear, distally 

 over the neck, ventrally over the face, and upward toward the eye, forehead, and the side of 

 the skull. The com-se of the development is indicated by the branches of the facial nerve. A 

 somewhat similar phylogenetic development is indicated by conditions found in the inferior 

 mammals and lower vertebrates. According to Ruge and Gegenbaur, the facial musculature 

 is to be looked upon as derived from two muscle-sheets, of which in man the deeper has dis- 

 appeared in the region of the neck while it is differentiated into the deeper facial muscles in the 

 region of the head. The deeper layer of transverse fibres in the neck, the sphincter colli, is found 

 in several of the mammals. The complex development of the facial muscles in man is char- 

 acteristic of the human species, and is associated with the use of these muscles as a means of 

 expression of the emotions, a physiological function superadded to the primitive function of 

 opening and closing visceral orifices. There is much individual variation in the differentiation 

 of the muscles. 



Fasciae. — The skin of the head and neck is, in most regions, firmly fused with the tela 

 subcutanea. This is composed of a dense fibrous tissue united by a looser areolar tissue to the 

 underlying structures. But a shght amount of fat is embedded in the subcutaneous tissue of 

 the scalp, forehead, and nose. Considerable fat may be embedded in the region of the cheeks, 

 the back of the neck, and the under surface of the chin (double chin). The constantly repeated 

 action of various muscles of the facialis group usually results by middle Ufe in the production 

 of permanent wrinkles due to alterations in the structure of the tela subcutanea and the cutis. 



The subcutaneous muscles of the cranial vault and the neck are invested with fascial 

 membranes. That covering the cranial musculature externally is firmly fused to the subcutane- 



* The pectoral muscles and the latissimus dorsi, which extend from the skeleton of the hmb 

 to the front and side of the thorax and the lower part of the back, arise frorn the hmb-bud during 

 embryonic development, are innervated through the brachial plexus, and will, therefore, be taken 

 up in considering the intrinsic musculature of the upper limb, p. 360. 



