REMOVAL OF THE BRAIN 217 



of the various foramina its outer layer becomes continuous 

 with the periosteum on the outer surface of the cranium, 

 whilst at the margin of the foramen magnum the inner layer 

 becomes continuous with the single layer of dura mater which 

 surrounds the medulla spinalis ; and that at the same level the 

 arachnoid and pia mater of the brain become continuous with 

 the arachnoid and pia mater of the spinal medulla (O.T. spinal 

 cord). Before terminating the survey of the interior of the 

 cranium the dissectors should revise their knowledge of the 

 blood vessels, and their relations to the dura mater ; and they 

 should remove the hypophysis (O.T. pituitary body) and in- 

 vestigate its naked-eye structure. 



Sinus Durse Matris. Four blood sinuses lie in the median 

 plane-, (i) the superior sagittal sinus in the upper or attached 

 border of the falx cerebri ; (2) the inferior sagittal sinus in the 

 free part of the lower border of the falx cerebri ; (3) the 

 straight sinus along the line of attachment of the falx cerebri 

 with the tentorium cerebelli ; (4) the occipital sinus in the 

 upper part of the attached border of the falx cerebelli. 



Two sinuses lie in a higher horizontal plane : these are the 

 spheno-parietal sinuses, which run along the posterior borders 

 of the small wings of the sphenoid bone. 



Six sinuses lie in a lower horizontal plane', (i) the two 

 cavernous sinuses at the sides of the body of the sphenoid ; 

 (2) the two superior petrosal sinuses along the upper angles 

 of the petrous parts of the temporal bones, in the anterior 

 parts of the attached border of the tentorium cerebelli; (3) 

 the horizontal parts of the transverse sinuses in the posterior 

 parts of the attached border of the tentorium. The terminal 

 parts of the transverse sinuses descend along the anterior parts 

 of the lateral walls of the posterior fossa. 



Two sinuses run obliquely downwards, posteriorly ', and later- 

 ally : these are the two inferior petrosal sinuses. 



Three sinuses run transversely connecting paired sinuses of 

 opposite sides: (i) the anterior intercavernous sinus in the 

 anterior border of the diaphragma sellae ; (2) the posterior 

 intercavernous sinus in the posterior border of the diaphragma 

 sellae ; and (3) the basilar plexus which connects together the 

 inferior petrosal sinuses across the upper surface of the basilar 

 part of the occipital bone. 



ALTERNATIVE METHOD OF REMOVING THE BRAIN. If it is thought 

 desirable to remove the brain entire by the more rapid but less instructive 



