1342 CLINICAL AND TOPOGRAPHICAL ANATOMY 



about 5 cm. (2 in.) above the opposite ear. (2) Kocher's point for draining the lateral ventricle 

 is taken over the frontal lobe 2.5 cm. from the median line and 3 cm. in front of the upper 

 Rolandic point. The needle is passed downward and a little backward to a depth of 4 or 5 cm. 



Up to this point the outside of the cranium has been mainly considered; it remains to draw 

 attention to some of the chirf points in the surgical analomy of the interior, especially ot the 

 base. The three fossae are of paramount importance in fracture. In the anterior fossa 

 the delicacy oi parts of the floor, the connection of this with the nose and orbit, and the exact 

 adaptation of its irregular surface to that of the frontal lobes, no 'water-bed' intervening, are 

 the chief points. Thus the slightness of a fatal fissiu-e, the frequent presence of bruising after 

 a blow perhaps on the occiput, which has been considered to have caused only concussion, the 

 characteristic palpebral haemorrhage, and the infection of a fracture here are all explained, 

 together with the possibilitj- and gravity of a fracture here from a severe blow on the nose. In 

 the middle fossa the frequency of fractures is explained by the facts that while here, as in the 

 other fossae, a fracture often radiates down from the vertex, the overlying vault being a region 

 often struck, the base is weakened by numerous foramina and fissures. Further, the resisting 

 power of the petrous bone must be lessened by the cavities for the internal ear, the carotid, 

 and, to a less degree, by the jugular fossa. For fluids to escape through the external meatus, 

 the dura, the prolongation of the arachnoid into the internal meatus, the membrani tympani, 

 and probably the internal ear, must all be injvu-ed. The presence of the middle meningeal artery 

 (fig. 1090) and the cavernous sinus in this fossa must also be remembered, especially in such 

 operations as that on the Gasserian ganglion. Posterior fossa: It is not sufficiently recognised 

 that fractures here are, owing to the anatomy of the parts, in some respects the most important 

 of all. It is here that a small fissure-fracture, ultimately fatal, with severe occipital and frontal 

 bruising and some intradural haemorrhage, has been so often overlooked, especially in the 

 drunken. This is explained by the supposed strength of the bone, this being really very thin in 

 places, by the thickness of the soft parts, and the abundance of hair. Further, there is no very 

 apparent escape of cerebral contents as in the anterior and middle fossae. Blood, etc., may 

 trickle into the pharynx far back, or a deep-seated ecchymosis coming up after two days, under 

 the muscles about the mastoid process, may call attention to the damage within. 



Dura mater. — The outer layer of this membrane acts as a periosteum, by bringing blood- 

 vessels to the bone while the inner layer supports the brain. The influence of its partitions and 

 its damping effect on vibrations is great in blows on the head. Its varying adhesions, according 

 to site and age, must be remembered. Thus while it is intimately connected over the base 

 with its adhesions to the different foramina, it is more loosely connected with the vault, as is 

 shown in middle meningeal haemorrhage. In early and later life the closeness of its connection 

 with the bones is also more marked. It is united to the inter-sutural membranes. 



Finally, the existence of the cerebro-spinal fluid with its power of lessening the evil of 

 vibrations and its aid in regulating intra-cranial pressure, must be borne in mind. The chief 

 collections, in which the subarachnoid meshwork is almost absent, are met with in front and 

 behind the medulla. That in front, also lying under the pons, Hilton's 'water-bed,' sends 

 a prolongation forward to the optic chiasma, but does not extend under the frontal or temporal 

 lobes. The collection behind lies between the medulla and under surface of the cerebellum. 

 Here, by the foramen of Magendie, the intra-ventricular cavities communicate with the sub- 

 arachnoid space of the spinal cord. 



THE HYPOPHYSIS CEREBRI 



The hypophysis (pituitary body) which has now become of great clinical 

 importance, consists of a pars anterior and pars intermedia derived from the 

 buccal ectoderm, and a posterior pars nervosa formed by a downgrowth from 

 the floor of the third ventricle. The gland lies in the fossa hypophyseos of the 

 sphenoid bone, and an enlargement of it, apart from general skeletal and nutri- 

 tional effect due to anomalies of its internal secretions, will cause pressure on 

 the cavernous sinus on each side, and on the optic chiasma above. It will also 

 expand the fossa hypophyseos, pushing down its floor at the expense of the 

 sphenoidal air sinus. Such enlargements may be detected by lateral radiograms. 

 The normal size of the adult hypophyseal fossa (fig. 1097) is 10-12 mm. from 

 before backward and 8 mm. from above downward (Keith). 



The hypophysis may be exposed surgically either by turning the nose to one side, and remov- 

 ing the upi)er part of the septum and floor of the sphenoidal sinus, or by Cushing's method, in 

 wliicli a siil)lal)ial incision is made in the vestibule of the mouth, and through it the mucosa is 

 then separated from each side of the nasal septum back to the sphenoidal sinus. A strip of 

 septum is removed, and also the floor of the sphenoidal sinus, after which the hypophyseal fossa 

 is opened and the gland exposed (fig. 1097).* 



THE FACE 



The topics included unch'r this heading are the arteries, parotid region, nerves, 

 mandible and maxilhi, orbit, mouth, palate and nose. 



The outline of the different hone.s — nasal, upper and lower jaws, zygomatic 

 • H. Gushing. The Pituitary Body and its Disorders, 1912. 



