134 



TOPOGRA.PHICAL ANATOMY OF THE 



adapted as to permit of free movements by which the head is flexed and 

 extended on the neck. There are two joint cavities — right and left — 

 corresponding to the two occipital condyles. Each is enclosed by a 

 loose joint ccjisule. The interarcnal ligament of the other vertebral 

 articulations is here represented by the strong dorsal atlanto-occipital 

 membrane (membrana atlanto-occipitalis dorsalis), which is attached to 

 the dorsal arch of the atlas and the dorsal margin of the occipital foramen 

 mao-num. The ventral atlanto-occipital niemhrane (membrana atlanto- 

 occipitalis ventralis) is not so strong, and fills the narrow^ interval 

 between the ventral arch of the atlas and the intercondyloid notch of 

 the occipital bone. Both dorsal and ventral membraoes are blended 

 with the joint capsules. A lateral atlantal ligament (ligamentum 



Ligg. alaria. 



J-Atlas. 



-- — Capsula articularis. 



— Epistropheus. 

 Longitudinal vertebral sinus. 



Lig. longitudinale dorsale. 



3rd cervical vertebra. 



Fig. 57. — The atlanto-epistrophic articulation, after 

 removal of the arches of the vertebrte. 



laterale atlantis) is connected with the joint capsule on each side, and 

 rims from the margin of the wing of the atlas to the jugular process of 

 the occipital bone. 



Dissection. — Remove the arches of all the cervical vertebrae, and then 

 remove the spinal cord by cutting across it at the foramen magnum. The 

 roots of the spinal nerves must also be cut. 



The spinal cord should be laid aside for later examination. 



Two ligaments are now revealed, namely, the dorsal longitudinal and 

 the alar. 



Branches of the vertebral and the cerebro-spinal artery (a branch of 

 the occipital) should be noted as they enter the vertebral canal by the 

 intervertebral foramina. 



A large vein or venous sinus {sinus vertebralis longitudinalis) should 

 also be observed on each side of the dorsal longitudinal ligament. The 

 right and left sinuses are connected by transverse anastomoses that run 

 underneath the narrow portions of the ligament. The sinuses are 



