406 THE MUSCLES AND FASCIA. 



Surface Form. The outline of the muscles of the head and face cannot be traced on the 

 surface of the body, except in the case of two of the masticatory muscles. Those of the head 

 are thin, so that the outline of the bone is perceptible beneath them. Those in the face are 

 small, covered by soft skin, and often by a considerable layer of fat, so that their outline is con- 

 cealed, but they serve to round off and smooth prominent borders and to fill up what would be 

 otherwise unsightly angular depressions. Thus, the Orbicularis palpebrarum rounds off the 

 prominent margin of the orbit, and the Pyramidalis nasi fills in the sharp depression beneath 

 the glabella, and thus softens and tones down the abrupt depression which is seen on the 

 unclothed bone. In like manner, the labial muscles, converging to the lips and assisted by the 

 superimposed fat, fill in the sunken hollow of the lower part of the face. Although the muscles 

 of the face are usually described as arising from the bones and inserted into the nose, lips, and 

 corners of the mouth, they have fibres inserted into the skin of the face along their whole 

 extent, so that almost every point of the skin of the face has its muscular fibre to move it ; 

 hence it is that when in action the facial muscles produce alterations in the skin-surface, 

 giving rise to the formation of various folds or wrinkles, or otherwise altering the relative 

 position of parts, so as to produce the varied expressions with which the face is endowed ; 

 hence these muscles are termed the "muscles of expression." The only two muscles in this 

 region which greatly influence surface form are the Masseter and the Temporal. The Masseter 

 is a quadrilateral muscle, which imparts fulness to the hinder part of the cheek. When the 

 muscle is firmly contracted, as when the teeth are clenched, its outline is plainly visible; 

 the anterior border forms a prominent vertical ridge, behind which is a considerable fulness, 

 especially marked at the lower part of the muscle ; this fulness is entirely lost when the 

 mouth is opened and the muscle no longer in a state of contraction. The Temporal muscle 

 is fan-shaped, and fills the Temporal fossa, substituting for it a somewhat convex form, 

 the anterior part of which, on account of the absence of hair over the temple, is more 

 marked than the posterior, and stands out in strong relief when the muscle is in a state of con- 

 traction. 



MUSCLES AND FASCLE OF THE NECK. 



The muscles of the neck may be arranged into groups corresponding with the 

 region in which they are situated. 



These groups are nine in number : 



1. Superficial cervical region. 5. Muscles of the Pharynx. 



2. Depressors of the Os Hyoides 6. Muscles of the Soft Palate. 



and Larynx. 7. Muscles of the Anterior Ver- 



3. Elevators of the Os Hyoides tebral Region. 



and Larynx. 8. Muscles of the Lateral Ver- 



4. Muscles of the Tongue. tebral Region. 



9. Muscles of the Larynx. 



The muscles contained in each of these groups are the following : 

 1. Superficial Region. Lingual Region. 



Platysma myoides. 4. Muscles of the Tongue. 



Sterno-cleido-mastoid. Genio-hyo-glossus. 



Hyo-glossus. 



Infra-Jiyoid Region. Lingualis. 



2. Depressors of the Os hyoides and Stylo-glossus. 



Larynx. Palato-glossus. 



Sterno-hyoid. 5. Muscles of the Pharynx. 



Sterno-thyroid. Constrictor inferior. 



Thyro-hyoid. Constrictor medius. 



Omo-hyoid. Constrictor superior. 



Stylo-pharyngeus. 

 Supra-hyoid Region. Palato-pharyngeus. 



3. Elevators of the Os hyoides and g. Muscles of the Soft Palate. 



Larynx. Levator palati. 



Digastric. Tensor palati. 



Stylo-hyoid. Azygos uvulae. 



Mylo-hyoid. Palato-glossus. 



Genio-hyoid. Palato-pharyngeus. 



