GENERAL TOPOGRAPHY 



793 



While there is a considerable subarachnoid space, the brain more nearly fills its 

 cavity than does the spinal cord. 



The average length of the brain is about 165 mm. and its greatest transverse diameter 

 about 140 mm. It averages longer in the male than in the female. Exclusive of its dura mater, 

 the normal brain weighs from 1100 to 1700 gm. (40-60 oz.), varying in weight with the stature 

 of the individual or with the bulk of the tissues to be innervated. Its average weight is 1360 

 gm. (48 oz.) in males and 1250 gm. (44 oz.) in females. It averages about fifty times heavier 

 than the spinal cord, or about 98 per cent, of the entire cerebro-spinal axis. In its precocious 

 growth it is at birth relatively much larger than at maturity. At birth it comprises about 13 

 per cent, of the total body-weight, while at maturity it averages only about 2 per cent of 

 the weight of the body. Its specific gravity averages 1.036. In proportion to the body- 

 weight the brain-weight averages somewhat higher in smaller men and women. Some very 

 small dogs and monkeys and some mice have brains heavier in proportion to body- weight 

 than man. 



The minimal weight of the adult brain compatible with human intelligence may be placed 

 at from 950 to 1000 grams. Above the minimal, there is only a general relation between the 

 degree of intelligence and the weight of the brain, owing to the fact that several factors may be 

 coincident with large brains. It may be said in general, however, that the average brain weight 

 of eminent men is above the general average. Some men judged eminent have had brains weigh- 

 ing less than the general average. Of the records generally accepted, the greatest brain weight 



Fig. 624. — Mesial Section of the Head of a Female Thirty-five Years Old . 



Superior sagittal 

 sinus 



Corpus callosum 



Septum 



pellucidum 



Thalamus 



Vein of Galen 



Epiphysis 

 Posterior cere- 

 bral artery 



Corpora 

 quadrigemina 



Third nerve 



Straight sinus 



Cerebellum 



Occipital sinus 



Fourth ventricle 



Sulcus cinguli 



Fornix 



Foramen of 

 Moiuo 



Crista galli 

 Anterior cere- 

 bral artery 

 Optic chiasma 



Sphenoidal 

 sinus 



Hypophysis 



Pons 



Medulla ob- 

 longata 



for eminent men is 2012 grams, recorded for the poet and novelist, Ivan Tourgenieff. The trust- 

 worthiness of this weighing is doubted by some authorities. From the undisputed records the 

 following may be taken: Cuvier, 1830 grams; John Abercrombie, 1786 grams; Thackery, 1658 

 grams; Kant, 1600 grams; Spurzheim, 1559 grams; Daniel Webster, 1518 grams; Louis Agassiz, 

 1495 grams; Dante, 1420 grams; Helmholtz, 1440 grams; Goltz, 1395 grams; Liebig, 1352 grams; 

 Walt Whitman, 1282 grams; Gall, 1198 grams. In the average brain weights for the races that 

 for the Caucasian stands highest, the Chinese standing next, then the Malay, followed by the 

 Negro, with the Austrahan lowest. 



The differences between the meninges of the brain and those of the spinal cord occur chiefly 

 in the dura mater. (1) The dura mater is about double the thickness of that of the spinal cord, 

 and consists of two closely adhering layers, the outermost of which serves as the internal peri- 

 osteum of the cranial bones, while that of the cord is entirely separate from the periosteum 

 lining the vertebral canal. (2) The inner layer is duplicated in places into strong partitions 

 which extend between the great natural divisions of the encephalon. Of these, the sickle- 

 shaped falx cerebri extends between the hemispheres of the cerebrum, the crescentic tentorium 

 cerebelli extends between the cerebellum and the overlapping posterior portion of the cerebrum, 

 and the smaller falx cerebelli occupies the notch between the hemispheres of the cerebellum. 

 Contained within these partitions of the dura mater are the great collecting venous sinuses of 

 the brain. These will be considered in the more detailed description of the cranial meninges. 



General topography. — In its superior aspect or convex surface the encephalon 

 is oval in contour, with its frontal pole usually narrower than its occipital pole. 



