THE FASCIiE AND MUSCLES OF THE HEAD 255 



with the posterior deep pectoral muscle to the medial tuberosity of the humerus. 

 Posteriorly it forms a fold, which, covered by the skin, forms the fold of the flank, 

 and ends on the fascia above the stifle. The dorsal limit of the muscle corresponds 

 approximately with a hne drawn from the posterior angle of the scapula to the fold 

 of the flanlc. Ventrally the two muscles are about a handbreadth apart in the um- 

 bilical region. Further forward they diverge, so as to overlap the posterior deep ' 

 pectoral muscle only to a small extent. Here the cutaneous muscle is closely ad- 

 herent to the pectoral and contains the external thoracic vein. Posteriorly they 

 diverge to the fold of the flank. 



The muscle is in general closely adherent to the skin and its contraction twitches 

 the skin, thus getting rid of insects or other irritants. 



The Fascle and Muscles of the Head 



The muscles of the head (Mm. capitis) may be divided into three groups, viz. : 

 (1) Superficial muscles, including the cutaneous muscle and those of the lips, cheeks, 

 nostrils, eyelids, and external ear; (2) the orbital muscles; (3) the mandibular 

 muscles; (4) the hyoid muscles. 



The superficial fascia forms an almost continuous layer, but is very scanty 

 around the natural orifices. It contains a number of the thin superficial muscles, 

 so that care must be exercised in removing the skin. Over the frontal and nasal 

 bones the fascia blends with the periosteum. 



The deep fascia is of special interest in three regions. The temporal fascia 

 (Fascia temporalis) covers the temporalis muscle, and is attached to the parietal 

 and frontal crests medially, and to the zygomatic arch laterally. The buccal fascia 

 (F. buccalis) covers the buccinator muscle and the free part of the outer surface of 

 the ramus of the mandible. It is attached to the facial crest, and posteriorly it 

 forms a band (Raphe pterygomandibulare) which stretches from the hamulus of the 

 pterygoid bone to the mandible behind the last molar tooth. It is directly continu- 

 ous with the pharyngeal fascia (F. pharyngea), which is attached to the great and 

 th3Toid cornua of the hyoid bone and the thyroid cartilage of the larynx; it covers 

 the lateral walls of the pharynx, and blends dorsally with the median raphe of the 

 constrictor muscles of the latter. 



Cutaneus faciei. — This has been described (p. 254) . 



MUSCLES OF THE LIPS AND CHEEKS 



1. Orbicularis oris. — This is the sphincter muscle of the mouth; it is con- 

 tinuous with the other muscles which converge to the lips. It lies between the 

 skin and the mucous membrane of the lips, and is intimately adherent to the 

 former. Most of the fibers run parallel to the free edges of the lips and have no 

 direct attachment to the skeleton. 



Action. — It closes the lips. 



Blood-supply — Palato-labial, facial, and mental arteries. 



Nerve-supply. — Facial nerve. 



2. Levator nasolabialis.i — This thin muscle lies directly under the skin, and 

 chiefly on the lateral surface of the nasal region. 



Origin. — The frontal and nasal bones. 



Insertion. — (1) The upper lip and the lateral wing of the nostril; (2) the com- 

 missure of the hps. 



Action. — (1) To elevate the upper lip and the commissure; (2) to dilate the 



nostril. 



'Also termed the levator labii superioris alaeque nasi. 



