i6 THE SURGICAL ANATOMY OF THE HORSE 



medulla oblongata, which is easily recognised at a glance by the arbori- 

 sation of the white matter in this part of the brain. Running inwardly 

 between the cerebrum and the medulla oblongata is the ossific 

 tentorium. This is the bracket-like piece of bone which dips into the 

 cranial cavity from the deep aspect of the interparietal bone. It gives 

 attachment to the tentorium cerebelli and the falx cerebri, the former 

 being the process of the dura mater which projects downwards and 

 forwards, and separates the cerebral and cerebellar divisions of the brain. 

 Its inferior border arches over the crura cerebri. The latter is the 

 process of the dura mater which separates the two cerebral hemispheres. 

 It is attached superiorly to the parietal and frontal sutures and 

 anteriorly to the crista galli process of the ethmoid. Along its 

 superior border runs the superior longitudinal venous sinus, 

 whilst along its inferior boundary, which bridges over the corpus 

 callosum, is placed the inferior longitudinal sinus. 



Above the guttural pouch the anterior straight muscles of the head 

 run to their insertion into the tubercles on the inferior aspect of the 

 base of the cranium at the junction between the body of the occipital 

 bone and that of the post-sphenoid. 



The rod-like base of the cranium is cut through longitudinally, and 

 is represented in section. Near the anterior extremity of this base is 

 seen part of the sphenoidal sinus, the visible part being that hollowed 

 out of the right anterior half of the body of the pre-sphenoid. Pro- 

 jecting into the cranial cavity from its anterior extremity is the crista 

 galli process of the ethmoid, the superior portion of which is that part 

 giving attachment to the falx cerebri, and in the dried skull this part 

 may be seen on looking through the foramen magnum as a sharp edge 

 separating the two olfactory fossa\ 



The inferior portion of the crista galli process is articulated to the 

 plate-like piece of bone projecting from the anterior end of the body of 

 the pre-sphenoid, and which is called the rostrum. 



