24 TOPOGRAPHIC AND APPLIED ANATOMY. 



of blood-serum may escape through a torn tympanic membrane after injury without fracture; 

 it is, however, of relatively infrequent occurrence and scanty. 



After fracture of the posterior cranial fossa ecchymosis is sometimes observed in the posterior 

 triangle of the neck. 



Fractures of anterior fossas may be accompanied by disturbances of the sense of smell, 

 those of the temporal bone by disturbance of hearing or paralysis of the facial nerve. 



It must not be forgotten that in the comatose or very young, blood from the nose or mouth 

 may be swallowed and afterward vomited or passed at stool. ED.] 



In the region of the sella turcica there is only a relatively thin plate of bone separating the 

 sphenoidal sinus from the cranial cavity, and tumors originating in this sinus may encroach upon 

 the cranial cavity and lead to compression of the brain or of the nerves situated at its base. The 

 same is true of tumors proceeding from the ethmoidal cells, since these spaces are separated 

 from the cranial cavity only by a thin plate of the frontal bone on either side of the cribriform 

 plate (see Fig. 16). 



THE SCALP. 



The greater portion of the skin of the cranial region is covered with hair (see Figs. 6 and 7) 

 and differs in many respects from the skin in other portions of the body. It is not only specially 

 rich in sebaceous glands, which claim the attention of the practitioner as the starting-point of 

 many cutaneous diseases as well as of sebaceous cysts, but the customary layer of loose sub- 

 cutaneous tissue, giving the skin its mobility, is absent in this situation. In its place there is 

 present a firm subcutaneous stratum infiltrated with fat, which is directly continuous with the 

 subcutaneous tissue of the eyes and lids, thus explaining the readiness with which erysipelas of 

 the scalp extends to these parts. This subcutaneous stratum, together with the overlying skin 

 (epidermis and corium) and the underlying occipitofrontal aponeurosis, forms a firm layer, 

 usually spoken of as the "scalp," which may be readily torn away from the external periosteum 

 or pericranium before opening the cranial cavity. The scalp is bound down to the vault of the 

 skull by such a very loose and movable connective tissue, the subepicranial tissue, that it may be 

 readily pushed back and forth with the hand, or even by voluntary muscular contractions in some 

 individuals. The skin and the occipitofrontalis muscle, the tendinous portion of which bears the 

 name galea aponeurotica, are firmly attached to each other by tense connective-tissue fibers 

 (retinacula) which pass transversely through the subcutaneous stratum. 



The occipitofrontalis muscle is composed of a muscular and of a tendinous part. The 

 muscular part consists of an anterior, of a posterior, and of a lateral portion. The anterior 

 portion, the frontalis (see Plate 2), arises from the supraorbital margin and the skin of the eye- 

 brows; the posterior portion, the occipitalis, takes origin from the superior curved line of the 

 occiput ; the lateral portions may be supposed to consist of the rudimentary attrahens, attollens, 

 and retrahens aurem, which are attached to the auricle. The tendinous portion is firm and dense 

 upon the vertex, but loses these characteristics at the side of the skull, where it overlies the tem- 

 poral fascia and is attached with it to the zygoma or is continuous with the parotid and masse- 

 teric fascia below. 



The dense subcutaneous tissue and the firm connection of the skin with the aponeurosis upon 



