872 HUMAN ANATOMY. 



backward, gradually increasing in size, to the junction of the falx with the tentorium 

 cerebelli, where it opens into the straight sinus. It receives small tributaries from the 

 falx and sometimes also from the corpus callosum. 



4. The Straight Sinus, — The straight sinus (sinus rectus) (Fig. 756), also 

 unpaired, lies along the line of junction of the falx cerebri with the tentorium cerebelli. 



. It is formed at the anterior border of the tentorium by the junction of the inferior longi- 

 tudinal sinus and the great cerebral vein {ve?ia Galeni) (page 877), and is directed 

 backward to open into the torcular Herophili or more usually into the left lateral 

 sinus. 



In addition to the two trunks by whose union it is formed, it receives a number 

 of small branches from the tentorium, branches from the posterior portion of the 

 medial surfaces of the cerebral hemispheres, and sometimes a median superior cere- 

 bellar vein. 



5. The Occipital Sinus. — The occipital sinus (sinus occipitalis) (Fig. 757) is 

 an unpaired, or in some cases a paired, sinus which descends from the torcular Herophili 

 along the line of attachment of the falx cerebelli to the posterior border of the foramen 

 magnum. There it divides into two trunks, the viarginal sinuses, which pass 

 forward along the margin of the foramen magnum, one on one side and one on 

 the other, to open into the bulbus superior of the corresponding internal jugular 

 vein. 



The occipital sinus receives as tributaries branches from the falx cerebelli and 

 the adjacent portions of the dura, and also some veins from the inferior surface of the 

 cerebellum. At the posterior border of the foramen magnum, where it bifurcates to 

 form the marginal sinuses, it makes connection with the veins of the posterior spinal 

 plexus. 



Variations. — The occipital sinus is occasionally wanting, and frequently extends only as far 

 as the posterior border of the foramen magnum, the marginal sinuses being undeveloped. It 

 may open above into either the right or left lateral sinus, or into the straight sinus a short 

 distance before its termination. 



6. The Cavernous Sinus. — The cavernous sinus (sir.us caverncsus) (Fig. 757) 

 is a paired sinus of considerable size which extends along the sides of the body of the 

 sphenoid bone from the sphenoidal fissure in front to the apex of the petrous portion of 

 the temporal. It measures about 2 cm. in length and has a diameter of about i cm. 

 and is almost quadrilateral in cross-section. Its external diameter does not, however, 

 represent the actual capacity of its lumen, since this is greatly reduced in size (i) by 

 being traversed by numerous trabeculae from which fringe-like prolongations hang 

 freely into the blood-current, a section of the sinus having very much the appearance 

 of a section of the corpus cavernosum penis, whence the name bestowed upon it by 

 Win.slow ; and (2) by the fact that the internal carotid artery and the abducent 

 (sixth) nerve traverse it, while certain other of the cranial nerves are embedded in its 

 outer wall. These nerves are the oculomotor, the pathetic, and the ophthalmic and 

 maxillary divisions of the trigeminus, which lie in that order from above downward. 



Tributaries. — At the sphenoidal fissure the cavernous sinus receives the ophthahiiic vein 

 and, farther back, occasionally the basilar vein, both of which are described later on (page 877). 

 In addition, it receives veins from the neighboring portions of the dura mater, and has connecting 

 with it the spheno-parietal and the intercavernous sinuses. These latter are transverse sinuses 

 which pass across between the two cavernous sinuses, the one (sinus intercavernosus anterior) 

 passing in front of the sella turcica and the other (sinus intercavernosus posterior) behind that 

 cavity, and they receive branches from the dura mater and from the pituitary body. The two 

 sinuses, together with the portion of the cavernous sinus between their terminations on each side, 

 form what is usually termed the circular sinus (sinus circularis). 



Besides the vessels which are truly tributaries, the cavernous sinus also has connected 

 with it certain vessels which are emissary in function, leading blood away from it. The two 

 petrosal sinuses in which it terminates are of this nature. In addition, veins pass from its under 

 surface (i) through the foramen ovale, along with the mandibular division of the trigeminal 

 nerve, to communicate with the pterygoid plexus; (2) through the fibrous tissue which closes 

 the foramen lacerum medium ; (3) through the foramen of \'esalius, when this exists ; and (4) 

 occasionally through the foramen rotundum with the maxillary division of the trigeminal nerve. 



