LATERAL PART OF MIDDLE CRANIAL FOSSA 325 



Rectus Capitis Lateralis. The rectus lateralis arises from 

 the anterior part of the upper surface of the extremity of the 

 transverse process of the atlas, and is inserted into the under 

 surface of the jugular process of the occipital bone. It is 

 supplied by a twig from the anterior branch of the frst 

 cervical nerve. 



Removal of the Head and Neck from the Trunk. By the time that 

 the dissectors of the head and neck have arrived at this stage of their work, 

 the dissectors of the thorax have in all probability finished their dissection. 

 If this is the case, the head and neck may be removed from the trunk by 

 cutting through the vertebral column at the level of the intervertebral fibro- 

 cartilage between the third and fourth thoracic vertebrae. By this pro- 

 ceeding the upper three thoracic vertebras, with the attached portions of the 

 first, second, and third pairs of ribs, are removed with the neck. The 

 scalene muscles and the longus colli are. therefore preserved intact. 



THE LATERAL PART OF THE MIDDLE 

 CRANIAL FOSSA. 



The structures contained within the middle cranial fossa 

 may now be examined. In carrying out this dissection, the 

 head should be supported on a block so that the floor of 

 the cranial cavity looks upwards. The following are the 

 structures which must be displayed : 



1. Cavernous venous sinus. 



2. Internal carotid artery. 



3. Middle meningeal artery. 



4. Accessory meningeal artery. 



5. The two roots of the Trigeminal nerve, with the Semilunar 



ganglion and the three main divisions of the trigeminal 

 nerve. 



6. Oculo-motor nerve (3rd cerebral). 



7. Trochlear nerve (4th cerebral). 



8. Abducent nerve (6th cerebral). 



9. Internal carotid plexus of the sympathetic. 



10. Greater superficial petrosal nerve. 



11. Smaller superficial petrosal nerve. 



Dissection, The dura mater has already been removed from one half of 

 the middle cranial fossa, and on that side it is only necessary to differentiate 

 the structures which lie in the cavernous sinus ; on the other side the dura 

 mater must be stripped from the medial part of the lateral portion of the 

 middle cranial fossa. Enter the knife at the anterior clinoid process, and 

 carry it posteriorly to the apex of the petrous bone. This incision must go 

 no deeper than is necessary to divide the dura mater, and must be made 

 immediately to the lateral side of the openings in the membrane through 

 which the oculo-motor, the trochlear, and trigeminal nerves pass. It is 



