THE MEMBRANES OF THE BRAIN. 2Q 



an outer endosteal which forms the internal periosteum of the bones, and an inner which sends 

 off the dural processes, falx cerebri, etc. Between the two layers the sinuses are placed. ED.] 



[The dura mater is continuous through the optic foramen with the periosteum of the orbit, 

 through the foramen magnum with the dura of the cord, and through the various other foramina 

 at the base of the skull where nerves enter or emerge it sends processes. These facts, together 

 with its intimate attachment to the cranial bones, explain the frequency of dural involvement 

 secondary to external infections. ED.] 



Although some of its blood-supply is derived from the anterior, posterior, and small menin- 

 geal, and occasionally from a relatively large mastoid branch of the occipital, these are small 

 and practically insignificant, and the most important artery of the dura mater is the middle 

 meningeal (see Figs, i, 10), which comes from the internal maxillary, one of the terminal divisions 

 of the external carotid. It enters the cranial cavity through the foramen spinosum, runs forward 

 and upward along the great wing of the sphenoid near the squamosphenoidal suture, and, at a 

 varying distance from its point of entrance, while still in the basal region, divides into an anterior 

 and a posterior branch (see Fig. i). The former ascends just behind the coronal suture to the 

 posterior frontal region [accompanied sometimes by the sphenoparietal sinus, which may be 

 wounded either by the accident which has compelled manipulations here or by the manipulations. 

 Eo.]; the latter runs in an arched course almost directly backward over the squamous portion 

 of the temporal bone, giving off ascending branches which rest upon the internal surface of the 

 parietal bone. The middle meningeal artery and its ramifications are lodged in furrows upon the 

 inner surface of the cranial vault (see page 18). There is a rich anastomosis between the branches 

 of the artery. The vessel also gives off perforating branches to the scalp. 



Injuries o] the middle meningeal artery complicating fractures of the skull are justly feared. 

 Not only may there be considerable external hemorrhage, but, what is much more likely, the blood 

 may be poured out between the dura and the bone, into the subdural space, and, if the arachnoid is 

 also injured, into the subarachnoid space. In this manner there is produced a large hematoma 

 with pronounced symptoms of cerebral compression which demand operative interference, 

 trephining or chiseling open the skull, turning out the blood-clot, and ligation of the artery. As 

 the trunk of the artery is situated at the base of the skull and is reached only with great difficulty, 

 we are specially interested in the exposure of the regions supplied by the two branches, and 

 particularly in the exposure of the anterior branch, the one most frequently involved. Both 

 branches are found by means of the line of Kronlein (see page 37 and Fig. 13), which is drawn 

 backward from the supraorbital margin parallel with the zygoma. The anterior trephine opening 

 is then indicated by a point two fingerbreadths in front of the intersection of this line with a line 

 drawn at right angles to it through the external auditory meatus; the posterior opening should 

 be made two fingerbreadths behind the point of intersection. The posterior branch may also 

 be exposed two centimeters directly above the external auditory meatus. The lateral anastomoses 

 of the vessels make it necessary to apply a double ligature to the main branch affected. [The 

 line of Kronlein referred to by the author is drawn horizontally backward from the supraorbital 

 margin parallel to the line from the infraorbital margin through the external auditory meatus 

 known to English readers as Reid's base line. To expose the anterior branch of the middle men- 

 ingeal the trephine may be applied on the line of Kronlein from \\ to \\ inches, depending on 



