PRACTICAL CONSIDERATIONS : THE SCALP. 



489 



of the internal pterygoid plate of the sphenoid. It then descends upon the anterior 

 border of the pterygo-mandibular raphe, whence it passes forward along the body 

 of the mandible, above the mylo-hyoid ridge, as far as the premolar teeth. From 

 this extensive origin its fibres are directed forward to become continuous with those 

 of the orbicularis oris, also inserting to a certain extent into the integument of the lips. 



Nerve-Supply. — From the buccal branch of the facial nerve. 



Action. — The buccinator draws the angle of the mouth laterally, pressing the 

 lips against the teeth. When the cheeks are distended the muscle serves to com- 

 press the contents of the mouth, and plays an important part in mastication in pre- 

 venting the accumulation of the food between the cheek and the jaws, forcing it 

 back between the teeth. 



Relations. — Superficially with the bucco-pharyngeal fascia, which is separated 

 from the anterior part of the masseter and from the zygomaticus and risorius by an 

 extensive pad of fat, — the buccal fat-pad. This is prolonged backward into the zygo- 

 matic fossa between the temporal and pterygoid muscles, and is traversed by the facial 

 vessels and the buccal branches of the trigeminal and facial nerves. 



The buccinator is pierced from without inward by the parotid duct and by the 

 buccal branch of the trigeminal nerve on its way towards its distribution to the 

 mucous membrane of the cheek. 



PRACTICAL CONSIDERATIONS : MUSCLES AND 



CRANIUM. 



FASCIA OF THE 



The Scalp. — The Occipito- Frontal Region. — The layers of the scalp from 

 within outward are : 



I. The pericranitim — as the periosteum covering this part of the skull is 

 termed^closely invests the underlying bones and is firmly attached at the sutures 

 through which, so long as these remain ununited, it is continuous (intersutural mem- 

 brane) with the outer layer of the dura, — the endosteum of the cranium. A similar 



Hair-follicles 



Fibrous septa 



Outer compact bone 

 D 



Superficial fascia 



Aponeurosis 

 Subaponeurotic 



Pericranium 



'^'°' /" ... - Jl 



Jnner compact bone 



Superior longitudinal sinus 

 Portion ot frontal section of head hardened in formalin, showing layers of scalp, skull, and meninges. X 2%. 



Pacchionian bodies 



and more constant continuity exists through the foramina. As the dura is the chief 

 source of blood-supply of the cranial bones, they rarely necrose after accidents which 

 strip the pericranium from their surface fpage 237). Subpericranial effusions of 

 blood, or collections of pus, are limited and outlined by the lines of the sutures. 

 ' ' Cephalhaematomata' ' in this situation correspond in shape to that of one bone ; they 

 are commonly congenital, constituting a form of caput succedaneum, following head 

 presentations, and are then apt to be found over a parietal bone, since that region is 

 most exposed to pressure during child-birth. Tillaux suggests that in early life they 

 may be encouraged by the softness and vascularity of the cranial bones and the 



