

THE CKANIUM. 1365 



The transverse sinus may be mapped out on the surface by drawing a line, 

 slightly convex upwards, through a point a little above the inion to the asterion 

 (1-J in. behind and 1 in. above the centre of the external acoustic meatus) at, or 

 a little in front of, the point E, Fig. 1069, and thence in a downward and forward 

 direction to a point f in. inferior and posterior to the centre of the external acoustic 

 meatus, where it finally curves medially and forwards to open into the jugular 

 bulb, which occupies the jugular foramen. According to Moorhead the highest 

 part of the sinus lies a finger's-breadth above the middle of a line extending from 

 the inion to the middle of the external acoustic meatus. The anterior border of 

 the descending or mastoid portion of the sinus may be mapped out by drawing a 

 line VW from a point a finger's-breadth behind the post-auricular point of the 

 temporal crest to the anterior border of the tip of the mastoid process. In 

 wounds of the sinus the haemorrhage is very free, owing to the inability of its 

 walls to collapse, but the bleeding is easily controlled by plugging. 



Of the cerebral arteries, the middle supplies almost the whole of the motor area, 

 and one of its lenticulo-striate branches, which enters the brain at the anterior per- 

 forated substance, is called " the artery of cerebral haemorrhage " from the frequency 

 of its rupture in apoplexy. The extravasated blood involves the motor part of the 

 internal capsule. The postero-medial central branches of the posterior cerebral 

 artery, which enter the brain at the posterior perforated substance, supply the 

 thalamus and walls of the third ventricle ; haemorrhage from one of these branches is 

 apt to rupture into the ventricle. The postero-lateral central branches of the pos- 

 terior cerebral artery supply the thalamus, and when one of these vessels ruptures 

 the haemorrhage is apt to invade the posterior or sensory part of the internal capsule. 



Semilunar Ganglion. The topography of the semilunar ganglion is of im- 

 portance in relation to its surgical extirpation for trigeminal neuralgia. 

 The ganglion is situated in the dura at the apex of the petrous portion of the 

 temporal bone, at the medial part of the middle fossa of the base of the skull. 

 The surgeon reaches it by an extra-dural route through an opening in the anterior 

 and lower part of the temporal fossa immediately above the zygomatic arch. The 

 bone is removed down to or, even better, beyond the level of the infra- temporal 

 crest, which forms the boundary line between the lateral and basal portions of the 

 cranium. By temporarily resecting and depressing the zygomatic arch a portion 

 of the floor of the middle fossa, medial to the infra -temporal crest, can be 

 removed. The dura is separated from the fossa so as to admit of the ligature of 

 the middle meningeal artery immediately after its entrance into the cranium 

 through the foramen spinosum. By separating the dura still further in a medial 

 and forward direction, the mandibular division of the trigeminal nerve is exposed 

 as it enters the foramen ovale, and, after it, the smaller maxillary division, as it 

 passes in a forward and slightly downward direction to enter the foramen rotundum. 

 To expose the ganglion itself and the trunk of the nerve the dura is then carefully 

 separated in a backward and medial direction ; in doing this care must be taken 

 not to wound the cavernous sinus and the trochlear and abducent nerves which 

 lie in its lateral wall. The oculo-niotor nerve and the carotid artery are less 

 likely to be injured. The ganglion has a grayish-red colour and a felted surface, 

 while the portio major or trunk of the trigeminal nerve is almost white, and striated 

 longitudinally. After dividing the mandibular and maxillary divisions of the nerve 

 close to their foramina of exit, the ganglion is seized with forceps and removed by 

 twisting it away from its trunk and the first division. 



Ear. The skin covering the lateral surface of the auricle is tightly bound 

 down to the perichondrium, hence inflammations of it are attended with little 

 swelling but much pain. The posterior auricular artery, which ascends along the 

 groove at the posterior attachment of the auricle, is immediately anterior to the 

 incision for opening the tympanic antrum. 



The external acoustic canal, the general direction of which is medially, for- 

 wards, and downwards, possesses various curves of practical importance. The 

 highest part of the upward convexity, which is also the narrowest part of the canal, 

 '. is situated at the centre of its osseous portion ; beyond this the floor sinks to form 

 a recess in which foreign bodies are liable to be imprisoned. Of the two horizontal 



87 a 



