RELATIONS OF BRAIN AND CRANIUM 



903 



The Relations of the Brain to the Walls of the Cranial Cavity 



The precise methods by which the exact positions of the most important fissures, sulci, 

 gyri, and areas can be ascertained and mapped out on the surface of the head in the Hving subject 

 are fully described in Section XIII. Here, only a very general survey of the relations of the 

 brain to the cranial bones is given and from a purely anatomical standpoint. 



The parts of the brain which lie in closest relation with the walls of the cranial cavity are 

 the olfactory bulb and tract, the basal and lateral surfaces of the cerebral hemispheres, the 

 inferior surfaces of the lateral lobes of the cerebellum, the ventral surfaces of the medullajand 

 pons, and the hypophysis. 



Certain of these portions of the brain lie in relation with the basi-cranial axis, that is, with 

 the basi-occipital, the basi-sphenoid, and the ethmoid bones, while others are associated with the 

 sides and vault of the cranial cavity. Considering the former portions first, the ventral surface 

 of the medulla oblongata, which is formed by the pyramids, lies upon the upper surface of 

 the basi-occipital bone. More superiorly the ventral surface of the pons rests upon the basi- 



Fig. 711. — Drawing of a Cast of the Head of an Adult Male. 

 (Prepared by Professor Cunningham to illustrate cranio-cerebral topography.) 



External part 

 of parieto- 

 occipital 

 fissure 



Position of 

 frontal 

 eminence 



Lateral cerebral 

 fissure 



Transverse 

 (lateral) 

 sinus 



sphenoid, from which it is partly separated by the basilar artery and the pair of abducens 

 nerves. In front of the dorsum sellse the hypophysis (pituitary body) is lodged in the hypophyseal 

 fossa. Still further forward the olfactory tracts lie in grooves on the upper surface of the pre- 

 sphenoid section of the sphenoid bone ; and in front of the sphenoid the olfactory bulbs rest upon 

 the cribriform plates of the ethmoid. 



Posterior and lateral to the posterior part of the foramen magnum the lateral lobes of the 

 cerebellum are in relation with the cranial wall, resting upon the lower parts of the supra- 

 occipital and the posterior parts of the ex-occipital portions of the occipital bone, while anteriorly 

 each lobe is in i-elation with the inner surface of the mastoid process and the posterior surface 

 of the petrous portion of the temporal bone. The area of the skull wall which is in close re- 

 lationship with the cerebellar hemispheres m?y be indicated, on the external surface of the skull, 

 by a line which commences at the inferior part of the external occipital protuberance and thence 

 runs upward and lateral ward. It crosses the superior nuchal line a little beyond its centre, and, 

 continuing in the same direction, crosses the inferior part of the lambdoid suture and reaches a 



Eoint directly above the asterion (the meeting-point of the occipital, temporal, and parietal 

 ones); thence it descends, just in front of the occipito-mastoid suture, to the tip of the mastoid 

 process, and there turns medialward to its termination at the margin of the foramen magnum, 

 immediately behind the posterior end of the occiptal condyle. 



The basal surface of each cerebral hemisphere may be said to consist of two parts, an anterior 

 and a posterior, separated by the stem of the lateral cerebral fissure. The anterior part, formed 



