THE ANTERIOR VENA CAVA. 



695 



Fig. 387. 



The snhsphpnoidf/l ronth/p/>f.s (Fig. 387) extend on the sides of the body of 

 the sphenoid l)one and basilar process, from the base of the subspheuoidal 

 process to the condyloid fossa, concurrini,' in the closing- of the occipito-spheno- 

 temporal hiatus. They open at their middle portion into the coiTespondmg 

 cavernous sinus, by an oval aperture which the 

 internal carotid artery traverses in penetrating 

 into the cranium. The anterior extremity 

 terminates in a cul-de-sac. Posteriorly, they 

 communicate through the condyloid foramina 

 with the occipital sinuses. The vessels which 

 carry otf the blood from these confluents are 

 the pterygoid veins, and the anterior radicle of 

 the occipital vein. We know that the posterior 

 branch of the latter vessel removes the blood 

 directly into the occipital sinuses. 



b. The emergent veins of the spinal sinuses 

 present a more simple disposition. At each 

 intervertebral space arise several branches, 

 which more particularly make their exit by the 

 intervertebral foramina to join the neighbour- 

 ing veins ; in the cervical region, the vertebral 

 veins serve as a receptacle in this way for the 

 venous branches from the spinal sinuses ; in 

 the dorsal region, it is the spinal branches of 

 the intercostals ; in the loins, the analogous 

 l)ranches of the lumbar veins ; and in the sacral 

 region, the lateral sacral vein. 



As a whole, the venous system of the 

 cerebro-spinal centres presents a special physi- 

 ognomy. The veins arising from the nerve 

 substance or the meninges, instead of passing 

 immediately into the vein.s of the neck or head, 

 open at first into irregular cavities {sinuses) 

 established between the cranium and the mem- 

 branes enveloping the nervous centres, or ex- 

 cavated in the cranial walls. The blood collects 

 in certain of these cavities, named confluents, 

 whence the vessels go which finally open into 

 the deep or superficial veins of the cervical 

 region. There are, therefore, two stages be- 

 tween the veins of the brain or spinal cord 

 and the veins of the neck and face — the sinuses 

 and confluents. 



SUBSPHENOIDAL CONFLUENTS IN 

 THE HORSE. 



1, Middle part of the subsphenoidal 

 confluent (right side); 2, anterior 

 extremity of ditto; 3, j)Osterior 

 extremity in the subcondyloid cavity 

 of the occipital bone ; 4, one of the 

 pterygoid veins, discharging from 

 the confluent ; 5, 6, anterior radicles 

 of the occipital vein, discharging 

 from the confluent ; 7, posterior 

 radicle of the left occipital vein; 8, 

 occipital vein ; 9, 9, temporal veins, 

 discharging from the parieto-tem- 

 poral confluents ; 10, temporal 

 condyle; 11, tuberosity of the 

 tem[)oral bone; 12, styloid process 

 of tlie occipital bone ; 13, condyle 

 of ditto ; 14, atlas; 15, axis; 16, 

 rectus capitis anticus muscle. 



Axillary Veins. 



A general confluent of all the veins of the thoracic limb and of some from 

 the trunk, the axillary vein commences beneath the scapulo-humeral articulation, 

 towards the terminal extremity of the corresponding arterial trunk, accompanying 



