BLOOD-VASCULAR SYSTEM OF THE HORSE 



The ventral longitudinal or sagittal sinus (S. sagittalis ventralis) is much 

 smaller than the dorsal sinus. "^ It runs backward on the corpus callosum in the 

 concave edge of the falx cerebri, and joins the great cerebral vein to form the straight 

 sinus. It receives veins from the medial surface of the cerebral hemispheres and 

 from the corpus callosum. 



The straight sinus (S. rectus) proceeds from the junction of the ventral longi- 

 tudinal sinus with the great cerebral vein behind the corpus callosum. It ascends 

 in the falx cerebri, inclining backward, and joins the dorsal longitudinal sinus at 

 the confluens sinuum. 



The transverse sinuses (Ss. transversi), right and left, proceed laterally from 

 the confluens sinuum; they pass outward in the transverse grooves of the parietal 

 bones, enter the temporal canals, and are continued by the dorsal cerebral veins 

 to the superficial temporal veins. They receive the dorsal petrosal sinuses, veins 

 from the posterior part of the cerebrum and from the corpora quadrigemina, and 

 the posterior meningeal vein. The two sinuses are connected by the sinus com- 

 municans, which extends across the cranial vault in a channel in the base of the 

 internal occipital protuberance. 



The dorsal petrosal sinuses (Ss. petrosi dorsales) ascend in the tentorium 

 cerebelli and join the transverse sinuses near the internal opening of the temporal 

 canal. Each is the direct continuation of the vena rhinalis posterior and receives 

 the vena basilaris cerebri. There is sometimes an accessory petrosal sinus along- 

 side of the chief sinus, which is formed by the confluence of veins from the pons 

 and medulla oblongata. 



The occipital sinuses (Ss. occipitales) are situated in the dura mater on each 

 side of the vermis cerebelli. They communicate in front with the sinus communi- 

 cans, and one of them is continued posteriorly by the dorsal spinal vein. Each 

 sinus is connected by a communicating branch with the transverse sinus and with 

 the ventral petrosal sinus. The right and left sinuses are connected by anasto- 

 motic branches, so that the arrangement is more or less plexiform. They re- 

 ceive veins from the cerebellum, medulla oblongata, and diploe. 



The basilar system consists of the following: 



The cavernous sinuses (Ss. cavernosi) lie in the medial grooves of the root of the 

 temporal wings of the sphenoid bone at either side of the pituitary fossa. The two 

 are connected by a wide transverse branch, the intercavernous sinus (Sinus inter- 

 cavernosus), behind and below the posterior part of the pituitary body.^ Each is 

 continuous in front with the ophthalmic vein and below with the ventral petrosal 

 sinuses; it communicates also by small anastomotic veins with the basilar plexus. 

 The third, sixth, and the ophthalmic and maxillary divisions of the fifth nerve lie 

 along the lateral wall of the sinus. The internal carotid artery traverses the sinus 

 and is connected with its fellow by a transverse branch which lies in the inter- 

 cavernous sinus. An oval opening in the floor communicates with the ventral 

 petrosal sinus and transmits the internal carotid artery. 



The sinus is not subdivided by strands of fibrous tissue as in man, but a few delicate bands 

 attach the artery to its wall. 



The ventral petrosal sinuses (Ss. petrosi ventrales)' lie along the borders of 

 the basilar part of the occipital bone, enclosed in the thick dura which closes the 

 foramen lacerum. The anterior part extends about half an inch (ca. 12 mm.) 

 under the temporal wing of the sphenoid. Here communications exist with veins 

 in the pterygopalatine fossa. The posterior end is bulbous and lies in the condy- 



' It is also termed the vena corporis callosi major. 



' A small anterior intercavernous sinus may connect the two cavernous sinuses in front of the 

 pituitary gland. Mobilio states that he has seen the cavernous sinus having a blind anterior end, 

 the ophthalmic vein passing laterally to the ventral petrosal sinus. 



^ These are termed the subsphenoidal confluents by Chauveau and M'Fadyean. 



